That'd be a fine idea if there were only like, 5 Pokemon left to make Megas for. The problem is that even excluding Ubers we still got tens, possibly still a hundred+ to go. Filling in those blanks is gonna take a long time even with a FFA format unless we abandoned the slate formula entirely and just made it a free suggestion mod where the council decides what is added and what isn't.
If OP is feeling burnt out perhaps the mod can be put on hold for a while. If the passion doesn't come back after, say, a month or two then it's probably time to turn over ownership. This mod's popularity has endured for a long time now and I have no doubt someone would be willing to take over.