Allow non-citizens to place blocks within player-towns
Blocks placed by non-citizens may be taken by citizens.
As it is at the time of this post, if a town expands to gobble up blocks placed by non-citizens, (I'm assuming) they may be unable to reclaim their blocks or place any new ones on their structure. The Mayor may not want to grant that player citizenship, but doesn't want to steal their blocks either. This leaves the mayor in a pickle.
You may consider this suggestion complementary to the "Mayor Control" or "ownership area changes" suggestions.
Actually, if your house is gobbled by a town, you’re still able to pick it up and move it elsewhere, even if you’re a non-citizen :)