No building cap!
Crazy idea probably not the first to think of this.
Leave the map free and clear of all player builds.
Have the player earn a “base” feat that transports the player to a build area outside of the map, like the dungeons (or even another server, once the server transfer is implemented, and this server holds nothing but bases).
Basically, go to the world, gather, fight, loot, etc…etc…transport (like the maproom) to your base and build whatever you want. Invite other players or keep it open for all to see.
[Insert technical jargon and other development stuff that I don’t know about that make this impossible, but, I can dream]