A slightly different track:
I think the only way they are going to get Pathfinder folks back is if they bring Paizo along. If Paizo was happy with 5e and started releasing adventures and suchlike under 5e, their fans would likely follow.
In order to get Paizo along, I think they need to, primarily, go back to something closer to the d20 System Liscence than the GSL. They need to let people sell things compatible with the game in a way similar to the way people sold things in the 3e heyday: with complete internal control and absolute confidence of independence.
This is difficult for...anything owned by Hasbro, since Hasbro is currently
very concerned with IP issues. They're busy turning all their toys and games into movies and TV shows, some of which are good (especially those involving Lauren Faust!), some of which...well...involve Michael Bay. But ALL of which are probably much more profitable than the original line. D&D is mostly valuable for that -- the brand name. The ability to slap in on a board game, card game, movie, novel, or TV show, and instantly get the dorky blogosphere generating auto-buzz for it. And Hasbro is generally smart with this format shifting. Micahel Bay's Transformers may not be your cup of tea, but it IS very profitable.
So the primary bone of contention is that there must be an agreement so that third party publishers (or at least Paizo) can confidently make a sound business in supporting this theoretical 5e. Which seems difficult to do without easing up on the internal control of the brand. Which is difficult to do in an environment where the brand is more important than any individual thing produced under it. Theoretically possible, but difficult.
If they don't get that right, it doesn't matter what the mechanics are, or what the fluff is, or what the powers system is. If Paizo can't support 5e as a business, it will chug along with Pathfinder, and, if it continues its expanding trend, it will get at least as big as anything branded D&D.
I suppose when Paizo greenlights the cartoon series helmed by Genndy Tartakovsky, starring the iconics, or has BioWare making games with the PF brand, perhaps set in Golarion, we'll know that they've done good.
5e will only succeed (compared to a presumably weak 4e) if they can bring along Paizo, or undermine the company somehow.
Interestingly, if they bring Paizo back with a more open system, it'll prove one philosophy I heard during 3e true (can't remember who said it, though)...hmm....