Newer, nicer suburban houses will have delivery rooms with full size doors or locker-sized doors opening into a little box or closet. This will become a common feature once it's accepted as normal and not considered "ugly" by architects and home buyers.

LED's already made light fixtures smaller and more superficial/decorative, the actual light is a thin panel that doesn't get hot. Design trends haven't adjusted to this yet but will catch up.

I think living rooms will be smaller because family sizes are smaller and everyone has portable screens and people don't have fat TV's or media on shelves or things like that anymore. Tastes will catch up and they'll shrink over time. Likewise with more people spending time online there is less need for storage of random stuff. Also generational trends away from collecting and accumulating shit. So smaller closets.

Kitchens might grow or might shrink. With more disposable income people like to pretend they like to cook at home even though they don't hence all the upscale fixtures that trickle down into middle class wants. But actually if food costs shoot up due to resource scarcity and food becomes less good tasting because of government regulations on sugar or bans on meat because of the effect on the environment then why bother.

I think 1 or 2 bedroom detached houses with a one-car or no garage will become normal again in countries like the US. At one time many suburban homes were built like this in working class areas, but by the 1970s it was unthinkable to buy a house with less than 3 bedrooms and a two car garage. But if many more people are single or couples with no kids, then why do you need more than one or two bedrooms? With the cost of housing going up forever and becoming less affordable, I see these being an option. For middle class people who will never own a home in the future, there are these purpose built corporate owned for rent only small houses going up in my city already. Perhaps they will be available to buy in the future if you are higher income.

I think home sizes will diverge. There will be few medium sized homes built. All new dwellings will either be 1 or 2 bedroom rental apartments or cottages, and then a tiny minority will be massive homes with several bedrooms.

In large expensive cities, large houses >3 to 4k square feet are going to replace smaller older rental properties. In Chicago, Boston, they are gutting the inside of old 4 plexes and walkup apartments to be single residences. In Houston they tear down a 800 square foot wood frame house and put up a 3 floor townhouse that looks very urbane but is a kind of small mansion. Usually despite the size the household sizes in these areas is low, like 2 professionals will live in that big dwelling. Therefore population density will decrease while household sizes increase. Cities will have smaller but more affluent populations.

Meanwhile smaller, somewhat denser housing for the former middle and new working class will be mostly built in "exurban" areas of states like Texas or Florida that are fast growing. There won't be mass transit, or bike trails, or even park spaces, or any kind of neighborhood feeling or anything utopian of that sort. Just apartment complexes and for rent cottages next to freeways. This is because the top down development process by which capital from things like REIT's find its way into construction favors high-income high-amenity private master planned communities first, and these always grow in the furthest flung greenfield areas. Special utility and service districts have replaced municipalities and local government involvement in building infrastructure or providing services. Therefore all subsequent development of more affordable housing or light commercial happens in a haphazard fill-in-the-cracks manner alongside major roadways that have power lines or sewer lines to them already and there is no will or interest by a developer to sacrifice profit or viability of their project to make these places walkable or add true public spaces to them. Automated driving will likely make it possible to privatize roads (because you can charge a fee and deny access to a car that doesn't without a gate or booth) to the point where rights of way are only easements. And if these are privatized then pedestrians or bikes or vehicles that don't have an invitation or agreement would be barred as well. Long story short, the future won't be that urban. Also leaving home and mobility will be somewhat of a luxury for the working and middle class as prices of everything goes up.