Yeah, but Blizzard will never introduce a class into the game that overlaps spectacularly with existing classes. That's exactly what Demon Hunters do. Not only do they overlap with agility melee classes, they also overlap with Warlock abilities. Even the name overlaps with an existing class.
New players might confuse demon hunters and hunters. Sure, this may sound like a silly reason, but Blizzard has been very specific in their moves to make sure that new players can easily get acquainted with the game and find themselves in the area most appealing to them. Why would someone click “hunter” when they can click “demon hunter”. That would be similar to choosing “paladin” over “more-awesome-paladin” if it were an option.
---------- Post added 2013-05-15 at 11:30 AM ----------
I'm talking about Warlocks becoming the game's version of Demon Hunters, and a Tinker class entering WoW. Both are strong possibilities because both make sense given the current trajectory of the game.
Clearly Blizzard is dumping Demon Hunter attributes into the Demonology tree to make Warlocks a more appealing class. So it makes sense that eventually Warlocks will become even more Demon Hunter-like over the course of the next few expansions.
The Tinker and the Alchemist are the last hero units from WC3 that have no abilities present in WoW. Also they are thematically different than any other class in the game. In addition, a Tinker class just so happens to fit every class gap in the game currently. Unlike other class concepts, there wouldn't be any overlap with a Tinker-style class in the game.