Honestly, I think there's wayyy too much overthinking on this. Blizzard absolutely will not handcuff themselves with the idea that "if we implement a Tinker it absolutely has to be ranged!" or "...it absolutely has to be melee." Nor will they say that if it wasn't in a game that they released 18 years ago that they cannot make it in WoW. That would be utterly ridiculous game design. In a game where they can create, modify and retcon lore on a whim, there really aren't any "rules".
Their criteria is almost certainly something like:
1) Does it make sense in conjunction with, and enhance the content we are creating in the expansion? Tossing a Tinker in an expansion themed around traveling through the realm of the dead and seeing vampires and angels would be weird. Conversely, adding a Necromancer class in an expansion centered around Mechagon like content would be bizarre.
2) Do they have cool ideas on how to make the class unique? If they decided to make a Tinker class but couldn't brainstorm a really unique set of ranged abilities but had amazing ideas for a melee Tinker, you can bet your bottom dollar that you'd get a melee Tinker. And the reverse is equally true.
3) At the end of the day, the litmus test is "would this class be fun?" and that will guide their class development. This can mean different things as the state of the game is constantly in flux, and the development team is constantly changing, but if they take an idea that meets the above criteria byt still doesn't connect in a fun way, I'm pretty sure they won't implement it.
But arguing about a unit from WC3 being such and such a way means that a class based on it must absolutely reflect it is silly. No game design team is going to handcuff themselves on the design choices made in an 18 year old game that was made by different people.