We know neltharion is a dead end. Hardly any new players will ever start playing there again due to its death valley feeling. We also know that the cata demand is out there and the community is desperately trying to get the devs attention for over a year (nelth forum).
So heres my solution for you:
1. Open another seasonal cataclysm server which will receive a total wipe every year (arguable). We know cata has no longevity so people who actually enjoy playing cata can do that over and over again.
2. After every cataclysm season you transfer all the existing characters to the currently existing cata realm neltharion so that nobody will lose anything. This way we could enjoy cata from scratch over and over again and if we want to play our so beloved characters we can easily log into nelth. (In addition, this could eventually revive neltharion)
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This does require 0 coding from your end- you can't claim your devs are 2 busy to do that. Nelth in it's current state is completely fine (bugwise), especially once it lasts only 1(?) year.
Dungeons are very hard while on 4.0.6 patch and not only harder, but mechanicly more interesting. Raids are also hard at start of Cata and require alot of coordination. PvP is much more balanced at 4.0.6 because no broken PvE weapons and trinkets are in the game yet (ie: Guthlark, Axes etc). Also everyone has a chance to kill everyone. New battlegrounds are very very good, unlike SotA and Isle of Conquest where we do more PvE stuff than PvP. On 4.0.6 Baradin Hold dialy quests are a blast since the zone is small and there is always world PvP going on. I can keep going on and on but i think i pictured a point.
Conclusion: While i am for total wipe and restart, making anything else than 4.0.6 content would be a mistake and the server would end just like it ended now. There is no 4.0.6 content cata server and people love it. Lets not forget, while on 4.0.6 patch, WoW was at the highest peak ever in the history.
I am offering my help to the Warmane from the Database side, since i do have a masters degree in Informatics and WoW Database experience.