Allow players to transfer (with their stuff) between classic, new era and even jade.
Add an extra area on the territory map that allows transfer to classic ect
That way the player base won’t be split off from each other, there will still be plenty of maps for players to have their own space but the important thing will be that the player base isn’t segregated.
Any player who need their own segregated space can just rent a server on gportal
This kind of merge still leaves peoples bases and still leaves plenty of useable regions for when future players join the game. If you shrink everything down to squash everyone on a few maps then there won’t be as much space for new players in future