Like guildhalls perhaps (if you hire a good doorguard). Can buy door with lock, alarm and hire a guard
Can customize furniture and such

And if you get someone's housekey in RL you won't become an owner of house, right? You will just have one key.

Same can be done here. And it could crumble after some time.

Outlanders could burn them (with some restrictions). Thieves could really steal (not just BJ, trap/bind or wait for hours till someone will come to the Inn)
Wealthy ones can spend money one more way (quite interesting, I think)

Boost to RP. Cities are a bit more realistic. Now I can _really_ say "I was born in Galadon. Let me show you my house. It's here, quite a poor hat near river, but its my house" (no mom, though ).

So, another wheel in big mechanism of CF