To be honest, I think there should be a certain system of owning regions for the next map, so there are much less ruins and inactive regions.
Perhaps- they have to gather up active supporters to keep their town/city/etc. active, and before they begin constructing their regions. This way, there isn't just two people living in a city with thirty buildings. I'd say, at least-
5/8 citizens per village
9/12 citizens per town
13/16 citizens per city
At the least. I know there is only around 40 active players at the most, maybe even more if I'm wrong. But, just speaking my mind. I can't tell if this is a really good idea or a really bad idea, or if it even makes sense
¯\_(ツ)_/¯
This was one method we used in the past, you had to reach "active citizen" thresholds for full rights in getting transferred. It was really quite similar to what you suggested.
It didnt really work. This creates only the incentive to get people to sign on as active supports for the time being, it had little to no bearing on whether or not people actually continued either being active or supporting once the move had taken place. Cities that had more than enough people to reach their threshold encouraged their extra members to instead sign on with other allies who did not have as many they could claim. There were a couple other reasons too.
As a general rule I think that the proper solution set for this includes mostly carrot incentives as opposed to stick. If you dont want someone to transfer soemthing to the new map, offer them something in value in return.
For example, you could do something like, for those with large regions, if they dont get it transferred over and simply choose to get the plots refunded, they get 50% more money from the refund. This gives them something of value in return for their sacrifice, and enables them to get off to a quick start in the new map because theyve got extra capital.