If it’s going to happen it likely wouldn’t be until The Last Titan when there’d likely be more Titan and tech theming for the expansion. Which would likely be 4-5 years away.
Midnight is going to be all elf and void themed. Unless they’re going to significantly expand the blood elves’ magic-tech capabilities to be near par with the draenei and then base a class on that, at which point it wouldn’t really be tinkers.
Something I’ve been thinking about alongside my pitch for what types of things Tinkers can be and do is have it be a special class where you don’t get to pick your Primary professions and so they are forced to start out with both Engineering and Alchemy while also being unable to change or remove them.
Then you can integrate those professions to be a part of how the Tinker plays.
Of course other non Tinker classes will still have access to those professions, but it is specifically the Tinker class that gets extra bits that directly flow into how it plays.
i have no expectations one way or another. If they happen, cool, if not, cool.
TBH, we don’t need a wasted class spot for a profession (engineering) to be made manifest into a class where currently anyone can pick up engineering already and role play their tinker on any other class/race.
To address the “Engineering is already a profession” argument, I simply disagree that engineering is or will ever become a level that competes with a class fantasy that the Tinker could bring.
Below are some fantasy Examples as to what I think a Tinker class can become that is both unique to the current class lineup and is far beyond a simple profession can capture.
Link to my my original post detailing out more about the direction I would like to see…
Do I think they are coming? No, do I want them to come? Yes.
Who here hopes tinkers aren’t coming?
“Tinkers have always existed in Wacraft lore.”
I agree. They’ve also always existed in World of Warcraft. Engineering was here out of the gate.
im pretty sure quite a lot of people dont want tinkers in the game lol.
yeah cause it makes total sense for them to drop a new class mid expansion with no hype no external buildup no announcements other than the patch notes. and have to fit in balancing them and creating a talent tree for them make sure the armor class fits their models, coming up with new models, adjusting the class to all the races model riggings, coming up with new animations,new spells. all in less than 6 months.
except paladins can heal others.
priests wear cloth. 
There will NEVER. EVER. Be a tinker class. Give it up already. It’s been 20 years. The “tinker” class already exists. It’s called Engineering. And it’s a profession.
I would love a Tinker class, but I don’t think so. I don’t think there’s any chance of that. They said Hero Classes are going to be evergreen content, and I feel like any near-term to mid-term class additions are going to be new Hero Class trees, rather than a completely new class (with multiple completely new specs and multiple completely new Hero Classes of its own, and new armor that has to be made every tier).
That would be me
We aren’t getting a new class mid expansion.
At most we may get a new spec like Shaman Tank.
Also we went through this speculation back in BFA and it didn’t pan out.
My goblin wants to know ((Shush, Im gettin to it)) why he should hand over Gallywix to the gnomes Master Tinker? ((Dude I asked, put the bow down!!)) 
These Mechanics!
This is how I feel.
Primarily because it is a meme to say it, and then when someone provides even the most barebone of pushback to it folks jump to ad hominems, more memes, stating “But Warcraft used to be a RTS” as if that means anything, blatantly ignoring links providing factual information stating that “tinker” in the WoW universe is a title for engineers, and a huge myriad of other things like that.
It is the same thing as folks who want playable ogres, murlocs, high elves, and so many other races like those: it is all one big meme, that for some reason, some folks take extremely seriously.
… which is why folks like myself and most others who know this topic’s song and dance by heart simply tell people “then ask for a mech based class.” It can be inspired by engineering, and alchemy, as those two are popular requests … but it can’t simply just be engineering/alchemy and then leave it at that.
Which is what most people who parrot this meme end up doing.
Exceedingly few people thought that, and those who did were just ignorant beyond belief. There were some, me included, who viewed Garrisons as player housing since it was apparent at the time of development of WoD that the idea of Garrisons were supposed to be precisely that.
Now with the latest interview with Ion he says that wasn’t the case but that’s dubious. But still, it is an official statement so… it is the closet thing we can have to facts in regards like these.
Let me be clear: we will have more classes in the future, and a mech-styled fighter is entirely plausible to be in the works. It just ain’t going to be what folks are asking for because what folks are asking for is a meme with no substance. To bring it to life, substance needs to be added with several issues needing to be solved.
Some of the biggest ones being how to distance it from Engineering (and potentially Alchemy as well), as well as to include a background for it that works for more than just gnomes and goblins, and to make it distinctively different from the loosely tech-related class stuff that’s available right now in-game.
Since after all… you can be a hunter with a mechanical pet running around with engineering as your profession. So the “tinker fantasy” is available in-game, just not in a way that folks who scream “tinker” are willing to even acknowledge.
Some of the takes in this thread ha!
Engineering doesn’t satisfy meaningful gameplay, if you played the game you’d know that.
Hunter + mechanic pet + engi is for sure leaning hard into tech themes, love seeing them around, but it’s just lipstick on a pig. Nothing about its play is altered or relevant to tech. You’re still casting stuff like survival instincts, kill command, stampede, hunters mark, etc. etc. Pretending to be a tech class is not playing a tech class.
You can dress your warlock up to look like a priest but that does not make you a healer.