I don't understand the aversion to playerhouses in regards to expansion. I've seen UN referenced as being a cluttered mess, but UN also did it badly. A decent sized, albeit empty and moderately detailed overworld level could be designed deliberately with playerhouses/player made content in mind, slap link between the map and that, and it keeps everything concise, encourages player involvement, and expands the map with new things to look at without taking attention from real development - all while both being tidy and out of the way so player content isn't distracting or bothering people who don't like it. Someone could even be hired as a sort of QA, if you wanted to make sure the levels were up to snuff.