My primary deal breaker will be incompatibility with OGL content. 4e is largely incompatible to the extent that I need to do a lot of work to convert things, so if 5e is more of the same then that's going to be difficult for me. I already have my own homebrew based on the OGL, so I'm not eager to drop it and transition.
Another one will be lack of some kind of open license like the OGL. It doesn't need to be super permissive, just permissive enough that TPPs actually decide to hop on board en-masse like back in the 3rd edition days. I'll take the mountains of terrible content if it means that we get a few gems from third parties. This is especially important since third parties can focus on niche content that Wizards is likely to abandon in favor of the typical "PHB 2", "Complete X", etc.
Another thing will be lack of interesting new content. If all I'm getting is stuff I've had in every edition of D&D ever, I question what the incentive is for an upgrade. I want interesting rules options, classes, backgrounds, spells, monsters, and magic items. They perhaps shouldn't be "core", but I want something more than just the exact same stuff I have reprinted for 3-4 different editions!
Wizards has a mountain to climb, for sure. I'd love it if D&D became my go-to system for fantasy adventure, but I question how they're going to do that without upsetting one group or another.