Except it isn't a "fanwank".
Again, look at the previous expansion inclusions; Each one got their entire kit from WC3 and the Demon Hunters got additional abilities from HotS. Those formed the foundation of the class.
Now look at the Tinker's abilities from WC3; Pocket Factory, Cluster Rockets, Engineering Upgrade, and Robo Goblin.
Now look at the Tinker's abilities from HotS; Rock-it Turret, Deth Lazor, XPlodium Charge, Grav-O-Bomb 3000, and Robo Goblin.
Those are distinctly Goblin and Gnome-style tech abilities, and simply don't fit every single race. You think a Draenei is going to be using an ability called "Deth Lazor" or dropping Pocket Factories that are pumping out little robotic soldiers? Let's also not forget the claw pack;
There's also the Goblin Alchemist, which is supposedly the base for the Tinker healing spec. Again, it's Goblin centric;
Now there's always a possibility that Blizzard could expand on the concept and make new graphics and animations for other races. However, there's also the very real possibility that you'll see this class limited to Gnomes, Goblins, Mechagnomes, and possibly Vulpera (due to Goblin skeleton).
Why? Because it'd simply be easier to do, and to port over the existing Tinker (and Alchemist) abilities.
Demon Hunters were Elven centric, Monks were Pandaren centric. Tinkers by their nature are Goblin centric. So it stands to reason that the class will be on Goblin terms.
We'll see what happens one way or another.