Demon Hunters have numerous implementation problems. People tend to ignore those problems because they love the class. However, those problems are pretty huge, and glaring. Not only are the abilities wholly owned by another class, but the very name causes implementation issues because it can be confused with Hunters. Let it go, it isn't happening.
The Tinker will draw players because no other class is like it, and because technology classes ARE popular in fantasy MMOs. However, your argument that a class needs to bring in the lost WoW subscribers to be considered a possibility is a joke. It isn't lack of classes that has caused WoW's subscription base to erode, its the fact that WoW is almost 10 years old.So until you can explain how the tinker will draw players (1.3 to 3.7 million)I doubt you will see the class become a reality.