It'd be nice to be able to have one lord for multiple regions. For the badlands, at least. I wouldn't really want to see one dude lord of 4 cities, but if badlands are to become so bad that no knight would want to be sworn to them and that even lords would be poorer than rural knights, then maybe being lord or being a knight of a badland shouldn't exclude you from also having estates elsewhere.
One way to control this would be with population of estates: "nobles may have up to X peasants linked to their estates, and can pick up as many estates as they want until they reach this limit".
Just brainstorming here... 'cause leaving them lordless isn't an option in a realm that elects their lords. One day, an enemy will join the realm, join one of the spammed auto-referendums, and bring the region to the beighboring realm. On the other hand, putting a lord there sucks for him, as he'd lack the funds to participate in 90% of the game.