I think the "Idea" of a universal TF2 League would be benefical for all parties in theory, more admins, more people, bigger playerbase and - more attractive for sponsors to sponsor a league with 10000 players rather than one league thats restricted to one region with 1000 players, its not a bad idea, obviously you'd need seperate divisions per region but that would still be better than before.
Merging all leagues would also result in a lot of head clashes, I can imagine league fees are going to be a hot topic of discussion, whitelists, maps, formats, theres a lot to get through to make something like that happen, but is it possible? Yeah obviously.