@memokal There are conquest mechanics, and the rules for each city are known to be somewhat malleable. That is, those in charge can change to some extent what is allowed.
Most likely, fighting in a city would be something that would have to be specifically allowed. I imagine that good aligned cities would not allow it, by default, but... evil and neutral cities seem likely candidates.
As to living together in the same city, there are time limits on trips to different worlds. Whether there will be anything for settling down elsewhere, outside the specific race transformations, is... probably unlikely. At least, that is what I got from the discussions about travel between the worlds. If there is ever such a thing, humans would likely be the best candidates for moving. Which is... somewhat the worst thing for all races settling together. Maybe they will offer such a thing at some point, although it seems like a whole new issue with balance and powersets that would take a long of fine tuning.
Theoretically a group could support a player who wanted to try such a thing, and continually send them to the human realms... but the resources and effort involved under current understanding make that seem very unlikely. AND that player would still get booted and have to go back, along with potential lockouts from travel, over and over again. How long of lockouts, how possible it would be to constantly portal with big group support, etc. are unknowns unless an insider has a clue!