+1 even though im a town-less mayor i think its a very good idea to have the ability to set your entire town to one biome
+1 I really like this idea since sometimes you can only get your town in half the biome you want which leaves the other half of the town all weird. i have had that happen to me in the past lol. i also wounder why no one has thought of this idea so far.
I don't see a downside to this. I agree that it can be annoying to have a town with multiple biomes especially considering it can effect things like water, the look of dirt, etc.