Everything you typed here can be altered by Blizzard with a swipe of a pen. Like I said, if Blizzard can retcon Black Temple, a Novel, and Warlock lore to bring in Demon Hunters, the stuff you're talking about here is small potatoes if Blizzard wants to bring in such a class (that doubles as a race). Heck, Blizzard gave demonology warlocks the middle finger and forced them to reroll just so Demon Hunters could get metamorphosis in the following expansion. If Blizzard can do that, you're being silly if you think they wouldn't take a giant axe to some lore that people don't even care about anymore.
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Well there's plenty of reasons to have massive restrictions on a Tinker class. However, we've been down that road before, no need to go back down it again. My final word on that would be don't be surprised if Blizzard introduces a Tinker class and it's only 4 races tops.
Agreed.Sure, it could be another Covenant system. Or a class. There's a ton of ways that they could do it. We may get another round of Covenants next expansion, or never see the mechanic again. Who knows? The question pops up: "Do they want to dole out a tiny bit of juice to everyone, or pop in a whole lot of the good stuff into a select few?" Could go either way.