It would simply make no sense to glue Aahrus, Spawntown, Desertopia, Revolt City etc. together into one city. The landscape, the roads, the underground, the water, the building styles, literally nothing would fit together. And even then, our cities are already big and we might as well just end up with districts dominated by single people because I'm not really interested in some random person getting an idea to build a cobblestone furnace on the roof of Spawntown Town Center.
I like the way the current world is. I think it's cozy to have large areas of land available for everyone and connect them with long roads and rails, etc. I like the current atmosphere of the world and I think the region system lets people start over if they want to. If it means abandoning the old resources and settling a communal city in a remote place where we play together for a week or however long we find it fun, I might join, and in the end, we could connect the city with rails and roads or whatever we want to.
I don't really have much to say regarding the idea of cutting the cities out of the regions and stitching them together. It's simply not going to happen.