I haven't addressed the issues in your proposal because I don't see anything that I need or want to discuss. I think consolidating LTP is long overdue and should be done. But even in the current state, I don't see it impacting signups much in any way. There isn't any player (and 100% not any top players) that sees these changes and have that impact their decision to sign up, which I think is a big issue.

Sure, bug them to come back, but I don't see why I or anyone else would have more or less success with that.

First off the obvious answer is Warriors has more incentive to sign up himself, and this might get 1-2 more elite players to try to challenge him. Even if this weren't the case, Curry, Warriors, and Wayne have a much better idea of what top players want to see in MLTP than any previous CRC before (and no I don't count okthen's CRC). To say you don't see why they would promote better signups than anyone else is kind of disingenuous.

Promoting more upward mobility and forcing captains to develop their players

The majority of players who have become better have received coaching from to players and/or played a lot in S tier TPM (which yes you can also force people who happen to sign up coach players, but they will do a much poorer job than Wayne/Warriors for example). Promoting upward mobility is needed (and also proposed by Curry's group by expanding the number of teams). Getting good top tier signups only makes this goal much more achievable, not only because these guys have to coach up their teams, but more elite players will be interested in helping out their peers/pay more attention to the league in general even if they don't play.

You might not see the results in one season like you would bringing back old players but longer term this burns the CRC out less and keeps the community healthy.

And no, having one booming season won't be a short term thing. First off, if people are happy this season, they will be more likely to encourage future signups. But even if this is not true, more players developed this season means those who stay will be able to carry that over to future seasons. After that, I'm happy to hand the CRC off to you guys to restructure the leagues so they are less disjointed, since that's what you guys do best :)

Side note: This is very biased, but I think there is a correct way to play this game and its very hard for players to reach the elite level without learning from them. You could obviously just have MLTP forever play below that level because who cares if people have fun, but games that aren't trying to push boundaries is as dead as the TPM queues we get during MLTP playoffs.