I know memory issues are a thing, the game engine running FFXIV might not be able to properly render more items without having issues with culling but yea I'm definitely in the camp of at least doubling indoor slots inside for all sizes, my medium has it's basement blocked off by walls simple because i Don't have enough slots to decorate it. I like to leave aout 20 or more slots just for seasonal decorating.

Maybe some other adjustments could be made too, such as:
> things placed on tables/walls counted all together as one item with slot restrictions to how many things you can have on say on a partition/table/estate walls
> ability to turn on/off floors (say if you don't want a basement/top floor), with a warning if you have things in said floor or in space where they intersect such as on stair landings.
> ability for us to sink a bit more gil and "pay" for more housing slots
> maybe a flexible housing slot system where you gain more slots as long as you keep your plot, or get <3's from message book... (not good in this current climate where people who have left the game who didn't relinquish there plot still has their house with no auto-demolition in place since they halted it)
> ability to upgrade/downgrade interior instance (doesn't effect outside) so say you have a small house but you wanted the room of a mansion inside you could, but still be limited on the outside)

Would be nice for +10 more outdoor slots for all houses too, maybe even a way to have an actual indoor "garden" for apartments which allows you to place outdoor furniture, maybe like a balcony leading outside the apartment complex, could also have like an "apartment allotments" sort of thing though that would take more instances which I don't think they'd ever do.

There's so many things they could do then just add more wards. Imagine if we could buy an apartment, change the interior size to a mansion and have a balcony for outdoor furnishings. They might have to not allow things like a chocobos stable on the balcony. Would be nice to be able to teleport directly into a house/apartment then having to change instances (teleporting to housing area -> going into estate/apartment building -> going into a fc room/apartment room). Another thing that would be nice is if you had Personal Housing rooms too, maybe allow friends (or just tenants) to add rooms to it like an fc house/apartment building.

Being able to rearrange floors would be nice too, say you want a small house without a basement but a floor above instead/ maybe a 2x length room, maybe if we could rearrange features such as where stairs are, where estate and room inside entrance doors are. I wish it wasn't as limiting as it is, could be cool to have floor names/room names too, actual rooms would be nice too. There is so much they could do if they spent time on it.