I agree with almost everything you've written. The only reason I don't make suggestions like this is because I feel like from a design standpoint my suggestions would be entirely ignored. I've never actually seen someone's influence from a forum be reflected in a game, outside of maybe Warframe (which is why I'm actually kind of a massive fan of DE.)
I make suggestions like "just have a functional copy of an isolated plot in an instance" because it is probably the laziest solution. They barely have to create assets for that outside of a skybox(s) and some background, it would just be something that already exists in the game; isolated so players can actually have one. All they'd need after that is whatever UI, netcode, and servers to support that.
You are correct, if I could have a large in the form of instanced housing, (while being able to choose my exterior/interior, including the backdrop because I'd want it to be snowy) I would not care about "showing off" to people. I want people to be able to visit it, yes, of course, but I don't care about it being in a ward, especially because wards are essentially ghost towns 98% of the time. I can absolutely count the number of times on one hand that I've interacted with someone from the same ward as me, or anyone who happened to be passing by, and I'm not shy. Despite that, I also know there's an RP community, so whatever plots there are that RP venues exist at, typically will actually have people at them. That's why I'm not totally cool with "destroying the ward system." I'll acknowledge that if that was the price to pay, that would suck, but it isn't as if a visitable instaced RP venue with even more access control wouldn't be beneficial, either. It would have pros and cons. Overall, I would like compromise, just not the kind of compromise that leaves people out. (Which is why I said "hey, lottery sounds cool, but maybe don't just make it all lottery? how about leaving in relocation so people can work up to larger houses rather than buying one outright, as that isn't fair to everyone who participated in the old system")
The only thing I disagree with a little is this:
They would probably have to expand a bit of the geometry of the plots and such to fit all house types, but if it fits (even if it's not a ton of yard space) it's still preferable to the way it is right now. I don't really see why we shouldn't be able to, anyway. People would just fight over normal plots then, in that case. I think editing that might be easier than designing tilesets to slap together to make a customizable home with up to 4 floors, since fixing up one housing zone in its entirety would allow you to make sweeping changes for all houses across all wards per housing area (since the subdivisions are just rotated 90 degrees, I was unaware of this until about 2 years ago).
As far as FC's are concerned, giving people the option to have a company workshop and gardening without access to a house would probably go a long way as well, since there's absolutely people who make shell FC's and consume houses just to have access to more subs and airships; as those can bring in a lot of gil. It'd also be kind of useful if FC members didn't have to gil sink individually for apartments, but the apartments were bulk purchased in slots by the FC houses. It would probably draw people into FCs and get them to actually interact with their apartment