Nations should be able to claim settlements/outposts that don't require a mayor and can be managed by nation leaders / coleaders. They could be used to claim siege bases or other siege related towns which are not made to be lived inside of so there would be no need for a real mayor and would otherwise be held by a town holder usually. Each nation would be able to claim a certain amount of outposts based on your nation size e.g. 1 per 100 players in your nation.
-Upkeep for outposts would be taken from the nation bank
-They wouldn't be able to toggle unpeaceful
-Would be able to claim up to the size of your nation bonus

Since there are so many towns they don't require real mayors / residents this is a good solution e.g. Movecraft towns, Siege bases