I think it’s an extremely safe bet to assume the tank spec would be in an exosuit like what Mekkatorque or Gallywix or Gazlowe have, and a ranged dps spec that would function like Torbjorn from Overwatch (aka the traditional gun + turret + wrench) style.
They have the easiest template of their lives, as Final Fantasy 14, Warhammer Online, Maplestory, and Guild Wars 2 all have Engineer/Mechanic/Tinker archetype classes that they can use as a template. All of which are incredibly fun to play too.
3rd spec could be a toss up between a Mad Scientist Healer fantasy, or the Buzzsaw Shredder backpack Melee DPS style like Gazlowe is in Heroes of the Storm
Here’s a megathread I made on it that’s still going
You should check out that megathread, but in a detailed nutshell expanding on what others have said-
The Tinker class fantasy is effectively being a magic-less being that compensates for what they lack in strength or magics with their ingenuity via inventions and machines instead.
Some notable examples of Tinkers in WoW already are Gallywix, High Tinker Mekkatorque, Keeper Mimiron and more. Though the Tinkers were originally a Goblin/Gnome thing, pretty much every race has NPCs that are proficient with machinery as their primary ‘class’. The exceptions would be the Tauren, Night Elves, Worgen, Kul Tiran, and Troll races, but nothing says they’re incapable of learning. As such the class would most likely be for everyone, similarly to how Monk is, lore wise, taught to your character if you’re not a Pandaren.
The class would likely entail the use of exosuits for melee dps or tanking, turrets, flamethrowers, missiles, mini-mechs, and bombs for a ranged dps, and wild concotions and a very dr jekyll/mr hyde mad scientist fantasy for a healer spec