At the very least, I've thought that all the secondary professions should be shared among all your toons, as there wasn't any variation with what can be learned. I don't think there should be a gimme to all the professions, as if they become linked, then you can only be either Goblin or Gnomish Engineer, and that would probably upset people who have leveled both to have access to both. Another thing I would be upset with is losing the ability to use my profession cooldown for multiple characters that I have the same profession with (Xmute Master Alchemy, Tailoring, and LW).
Honestly, it's a double-edged sword, but if they worked out the cooldowns so that each toon would have its own internal cooldown per profession, and they flattened Engineering like they did with BS and LW where you don't have separate Goblin or Gnomish Engineering schematics, then I'd be on board. The only other issue I would see would be the specialization with Alchemy, and having the ability to change each toon's specialization.