Little chance of a Fifth Edition; Fourth still has a lot of legs under it, and sales have been very good even with the slow follow-ups. And bear in mind that WizKids still owns it; it’s FanPro that is losing the license, and the staff at Catalyst Game Labs will be similar to FanPro’s, but bigger.

I don’t think the d20 license being revokable is a big deal at this point — few publishers USE the d20 license anymore, even if they’re using material from the d20 SRDs. And the ones that do generally have strong enough brand names [I'm thinking of Goodman Games' Dungeon Crawl Classics here] that dropping the d20 logo from them likely wouldn’t impact their sales.

As for open systems that are catching fire, FATE, a Fudge-variant that powers many of the titles from Evil Hat Productions [most notably the pulp hit Spirit of the Century] seems to be the #1 contender at the moment, especially as it’s powering the upcoming Dresden Files RPG.

cheers,
Adam