Too strongly tied to trolls and voodoo to be realistically available to other races, not unique enough even if it was.
Mainly because its a broad concept. Its so broad that you don't even have to call it "Tinker". You can call it Technician, Mechanic, Artificer, Gyromancer, Inventor, or Machinist and it still works. People recognize that that level of broadness and flexibility is what Blizzard looks for when they determine classes.
It also helps that its unlike any other class currently in the game.
1 reason why shadow hunter isn't likely at all:
headhunter = warrior or rogue
which doctor = tribal shaman
dark ranger = undead hunter
Warlorcs of Draenorc made me quit. You can't have my stuff.
Nope, Shadow Hunter is a stupid idea, even worse than Tinker, which let's be honest here, is pretty fucking stupid.
Anything but another hunter class IMO lol..
would actually prefer shadow hunter way more then tinker, got more love for them from the WC3 universe.
Or a dark ranger maybe. Really annoys me that in all games, there is always only 1 bow user. Whhyyyyyyyy
paladins and Dks say hi
Most classes are not A + B classes but is just easier to explain it saying that is a combination of hunters and shamans, in that way most people could get the idea...
Cause Shadow Hunters use, elemental magic, nature magic, attack from the shadows, use bows, use daggers, use dark magic, etc..., so if you think about it is more like hunter + shaman + rougue + warlock + druid, so... it isn't a combination of classes, is just easier to explain that way
I will give you this: at least your new class fits thematically with the possible expansion it would be introduced with. You know; like the other two new classes were.
New classes won't just be pulled out at random just 'cuz people like it/want it.
"Oh you're fighting Azshara and her underwater legions and need some additional underwater warriors? Let's train some Demon Hunters!"
Gonna go with the Tinker here, because of its nigh limitless possibilities.