I'm not against tinkers (so long as the 'silly' elements are kept in check) but I am against people claiming that Tinkers are the 'only' option blizzard could go with for the next class and dismissing all other ideas out of hand. Not saying all tinker fans do this but some in this thread certainly have.
In reality though, there isn't at present a distinction between engineers and tinkers. Tinker is even a subset of engineering skills where you enhance your armor. Blizzard could create a difference if they made a tinker class, but at present there isn't really one except npcs are able to take it farther than players currently can, unlike say enchanting where there are different schools of arcane magic and enchanting is one of them, while mage player spells fall under something else. The only real difference is in terms of scale, a tinker is a more powerful engineer in the terms of what players are asking for in the class, while a mage is not just a more powerful enchanter, those are two different schools of arcane magic.
They certainly could make a tinker class if they want to, but I think it would be difficult to do so without A. infringing on the identity of the profession which has been around since vanilla and B. keeping the 'silly' elements toned done, like the robo arms coming off your backpack. The silly elements of brew master were quite enough for me I'd rather not see another repeat of that, but that's just me.