So as I was playing the game I was also thinking of what could be changed/improved/added. So get ready it will be a long one.

First off for some improvements/changes.
1.Grass shows up within the house. Not a big deal but it triggers my lazy OCD where I can see a grass where it does not belong (How does it grow in a dark basement that is poured with concrete?) and then couple of times I noticed as if I was able to mow a wee bit of it within the house. Again not a big deal but still.
2. Balconies and terraces should not count as "garden." Again not that big of a deal but still they should be separate. Several times I was frantically running around the garden within Lux DLC trying to find the trash and dirt just to find it later on on a balcony.
3.Fountains (and I am basing it on the one in the castle's courtyard) seem not to work. I mean the fish in the aquarium and ponds swim and there is animation on the water wall fountain that imitates the flow so maybe you could do so with all the fountains? And more ideas on it further on in here.
4.Object/color name check. Just in case you want to match something to what is already in the house but going through the list becomes a chore.
5.With blinds and curtains being able to adjust them for the particular window as to that they get less of a collision conflict with objects when installing (I mean you can always tuck the curtain behind or around it) and being able to take curtain "temporarily down" while painting.
6.Better Object manipulation. Say with doors you can rotate them so that the handle is on one side or another, but then it creates situation where the threshold is on one side or another and it looks weird. Why not rotate the threshold and then be able to switch handle's side? Or with some showers. Instead of choosing the "right or left side" from the tab, be able to rotate the glass alignment and then be able to q-flip where panels go.

Second a boatload of ideas (get either popcorn or headache meds, one of those will get usefull, Oh and if I use some of the user's ideas I apologize in advance, feel free to claim it ;) )
1.For the April's Fool joke create a duo of Helpers that for the day would do nothing but hang around wherever you are and crack jokes (but please no simple farts and burps. If you have to go there make it like in Warcraft 2 with 2 headed ogar unit where they burp and conversation goes Head1: "He did it!" Head2 "NO He did it!!" and then release DLC where they would actually do some work if ordered, in comedic fashion, and of course with some pay. And they could be called Hot Dog Helpers (refference to Black Dog Salvage businnes from Salvage Dawgs tv show (more on it later) as well as Hamburger Helper that is sort of cooking packet thing that often have spices and rice or pasta to be used with meat.) Of course they could be small and skinny leader and big and fluffyish duo.
Small would be called "Count" Louie-Napoleon C.P. De Money - De La Bonaparte and Burbon - d'Orleone XXI (Count De Money refference to Mel Brooks' History of the world, Louie, Napoleon and the rest of last name reference to French rullerls and C. standing for Charlemagne aand P for Philippe. where last name is sort of royal/nobility tracer name and all that. Maybe go wild and add how Polish names for women go if they want to display their last names after divorces with like "de domo" being for maiden name and then primo voto, secundo voto, etc that means within Poland "After first, second, etc husband.And XX! is roman numeral for 21 which would be a combined number of rulers of France that have had a name of Charlemagne, Napoleon, Louie, Philippe or Louie-Philippe together Eventually make it XXX if you add Charles as a form of Charlemagne and all that)
The bigger would be B. Johnny Von Smallhausen (B. would be for Bernaise (again reference to Brooks film. where B.Johhny would be reference to kids book called "Junie B. Jones" that I once upon a time came across where main characters B. stands for Beatrice, except she doesn't like that name, she just likes the B. in her name, Johnny would reference Johnatan, except he also prefers Johnny and Von Smallhausen would be reference to a character from Allo Allo series as well as Little John from Robin Hood. And maybe have crazy spelling on the last name with extra letters and some umlats/accents and all that fun.)
Ok that was a long one. Now to the rest.
1.Multiplayer. Maybe up to 4 people (I think I saw it somewhere out there, can't spot it right up.)
2.DLC based on floors, walls, ceilings, and roofs.. I saw that roofs are coming in Farm. But further dlc where we could do stuff with ceilings as well and maybe more creative designs on walls (horizontal and uneven strips as well as other designs) and maybe an "estimate" how much paint, tiles or panels to buy. Also adding 2 more wall building options. Have a floor based part wall as well as floor and ceiling partial wall next to ceiling partial and full walls.
3.Extensions and blueprints DLC. Again it does come in Farm to a degree but elaborating on it. Potentially also being able to use attics (turtle house to mind where there is this whole space under the roof we could renovate and potential in some houses to dig into the basement.) And with blueprints having the option to "draw" the plans on the ground not only minimap plus having the grid/line for ceiling lamps as well as the wall ones so they would be straight. (saw that bit somewhere)
4.Custom built houses (could be part of Blueprints DLC or a separate one making potentially even 3 DLCs one for Blueprints, one for extensions and one for whole houses.)
5.Ability to add custom built houses/extensions to workshop and maybe even some missions to them. Also adding to the game "follow up" missions under a premise of "hey remember me? you did such and such job for me. I need another favor."
6.Cleaners DLC (related to Hoarders DLC post here) where you would clean up a bigger job and maybe sift through the items and use them as part of either your income or toward job's budget. Where the found items you can either A.return to owner, B.Keep to yourself, C.Sell to store (least amount of money guaranteed instant sell) |D.Pawn Shop (more money potential but you need to barter with lesser guarantee) E.Sell online, retail price, but you wait some time (it would call for introduction of days into the game. But it could be a simplistic count like Monday, week 1 and on.) or F.Sell at auction with potential for biggest profit but also starting at the lowest and no guarantees.) It could have several parts like main DLC being general cleanups and side DLCs being based on Hoarders, Garage Gold and similar shows. And also having an appraisal/hunter guy whom you can pay to apprise the items or hunt for the client's request if you want to save on time, and make Hot Dog Helpers to do the sifting.
7.On similar note DLC based on shows like American Pickers (where a client sends you on a hunt for an item for his/her house and you need to visit several places, but you can also pick other pieces you would want) or Salvage Dawgs where your contract would be to salvage (often for yourself) a building (maybe random generator of such buildings) or Wisconsin Woodpeckers crew form Ax Men that was taking old barns apart for salvage materials. Maybe even hunting for sales on say paints and other materials where I could use some of mine and have bigger profit margin.
8.In relation to 6 and 7 warehouse ownership so you can store the salvage/bought items. And those you do not use on a job you could sell. Again mentioned earlier replayability under "hey remember me" would be great.
9.In relation to 8 being able to own your own warehouse and maybe office or "side business" next to the house would be cool. I know I know, you will say you can. But only one property classifies as "own" and the others are flips. I want an office (say in place from one of the high rises in Lux DLC) (where I can have a secretary and all that :P) and a separate warehouse for storage of my stuff from picks and salvage jobs that would be different from my primary residence and then having a summer and winter and vacation house and a yacht and a condo for my inlaws that would be visiting me :P (hey I can always dream. But having separate office and warehouse next to the house would be cool.)
10.Regionally based DLCs like Chinatown being Asian themed, Howling Fjords Scandinavian designs, Jackowo Polish (big Polish neighborhood in Chicago.) Etc. Maybe also like Victorian or Louisiana based within U.S.A.
11.On the go DLC. A DLC that would deal with boats, busses, RVs, Campers, Planes, Trains and anything that moves that could be converted to a house. Also with an ability to move the "house" from place to place (say different areas of the map) or be on the move and having a driver "working" for you ("pay" might be based on some fixed amount depending what/where you choose.)
12.Tiny Living based on small/minimalistic houses.
13.Going big. Basically opposite to 12. And say using the office scenario from Lux DLC instead of one floor having 3-4 floors. You want a castle? it's way bigger than the one we got now.
14.DLCs based on other shows like Treehouse Masters or Pool Kings (I think) or youtube channel of Greg Wittstock the Pond Guy where main part of a job would be said idea.
15. Other shows like house hunters where you tour say 3 houses with the buyer(s) and they "choose" one that you then renovate for them where you might "put an estimate" on what needs to be done in that house that would "influence" their decision (or not ;) )
16.DLCs based on other games like castle flipper or Monument flipper where you take on such jobs as renovating a historic castle or (re)building a church or mosque or other temple, or flip such into residence.
17.We Bought a Zoo DLC. BAsically being able to expand your farm with more "exotic" animals or pets.
18.Back in Business where you renovate/flip businesses and maybe have "side businesses" that while they would bring income it would be rather small.
19.Abandoned Towns where you could get an abandoned town or help somebody with it.
20.Chateau similar to castle flip (I thin should be 2 DLCs just for the style difference between castles and Chateaus.) but it can contain Palaces.
21.Back in Time where you go for more historic buildings.

Ok I do not remember any more sins. And still think I dumped out quite a lot. Hope I won't get stoned for my craziness ;)

Couple of other things that came to my mind since I originally posted it.
1.Being able to move items between houses you own (might come with warehouse idea I mentioned.) What do I mean? Being able to bring the puzzle from the Turtle House to Dracula's Castle and be able to make it day there (whaaa?)

2.Based on Let It Snow house I noticed when I left the room the lights went out. Not sure if it was just me or it's a bug related to that house or the original intention but at times it was annoying (very mildly, but still) even when I went between living room, dining room and kitchen areas that in the end are open plan (and I changed nothing) or when I went on a scaffolding because I wanted to repaint some walls above or put some decorations there.

3.Considering "tall" rooms that are taking up two floors be considered as one room so we could put chandeliers and other lights that would be controlled by same floor switches, as well as the dirt show up for one floor not two. Now the staicases that have the landing could be considered as a separate floor. But I am certain it could be done.