I think a lot of people stopped playing simply because of the map change. Not that i think the new one is bad, i was excited for it and i still enjoy playing on it. but considering barely anyone plays on all the disabled servers, maybe one or two servers (one being enabled,one being disabled) could have the old map.
(Ender Chests items would probably need to be seperated of course.)
Welcome on the forum! As for TMD, their would be less servers after the update. TMD-realist, TMD- (forgot the name but I think it was hardcore), TMD-2, TMD-3, TMD-4. I don't know if Havoc plan to keep their TMDPRC-1 server open.
There is an issue community have discussed about qte of server that could apply to your suggestion. Before, community was divided between TMD-OP, and TMD-1. The main purpose for the new server names, would be to have more players on the same server at a time (150), and a less divided community.
As for your suggestion, I also was wondering if they could keep a server for the current map. I guess it would depend on server popularity, after the TMD update