The lynchpin for me will probably be the casters. If they give muggle classes the 4-page class treatment and bloat a hundred pages of caster options like they did in AD&D, 2nd Ed, and 3.X (and Pathfinder continues to do) then I probably won't bother. 13th Age already figured out the solution there, as well as an elegant handling of skills / backgrounds. Almost anything 5E brings to the table right now can be ported over to 13th Age with minimal fuss and none of the stupid Magicians-over-Grogs dichotomy that soured so many D20 editions. Sure, a ream of spells is a great way to pad page count and move splat-books, but honestly, that tradition of "worst-to-first" casters sold nerdy little kids like I was on games and novels but it made for lousy cooperative game design. I want another edition of D&D that admits that was a horrible mistake and continues to evolve into a party-centric game at all levels.
Kender, Psions, and silliness like goofy armor and weapon disparities and a uselessly inflated "Gold Standard" on currency are all pet peeves rather than deal-breakers.
I guess the real issue for me will be whether there's any value in using 5E for anything more than expansion fodder to 13th Age.
- Marty Lund