I'd just be mean and make the features directly dependent on how many people benefit from the house, rather than the type of house -
If you have a lot of co-owners of your private house, you get joint access to stuff like gardening and ultimately airships, whereas living alone just gives basic decoration rights. Same would apply to FCs - very small or even one-person FCs would not gain access to all the features.

With housing being a very limited ressource, that would set a clear incentive to share it with as many people as possible :3

But people would have my heaaad if that happened :P