There's no reason why there can't be a body with a built-in EVF and one without.
If Canon (or Canon USA, at least) is having trouble pushing one model, how will they feel about two? The other problem I see with that is that I'm afraid the two models will have different sensors - a cheap one (T5i/SL1 sensor, no EVF) and a more expensive one (70D sensor, EVF, and bigger).
I think your guess is right...and I do wonder about the wisdom of such a choice.
The #1 attribute of the M is its sensor size...huge relative to its body.
The #2 attribute of the M is the body's small size...which makes the 22mm pancake a winner.
The #3 attribute of the M is its 11-22mm lens, which brings above-average, image-stabilized, Canon-branded wide-angle shots to hobbyists at a very reasonable price
But the 18-55mm lens is actually pretty good, too, and it is better for video than the 22mm because of IS. I own a second-generation Rebel, and it and its kit 18-55mm lens is jumbo-sized compared with the M with its 18-55mm attached.
So, I would be less inclined to buy an M that is (substantially) physically larger...I would just rather use one of my DSLRs instead.
The EVF, in my view, might sell more bodies to the holdouts out there, but my gosh I have certainly gotten used to shooting M-style...so much so that I occasionally find myself reaching for my DSLR's LCD screen! So an EVF inclusion that makes the M's body larger? Or even just a little bit larger? I vote no.
...on the other hand, a movable, tiltable LCD screen for the M? If that could be done (with minimal enlargement of the body)...I might buy into that.
But this two-different-model solution to fix what ails M sales? I don't know. It sure might confuse the public.
Here is what Canon needs to find out...how much will their base pay for 70D-quality focusing on an M body? If you think about it...it is a really fascinating question.
Would Canon move product by selling such an M...for the same price as the 70D? I don't think so.
If the 70D is $1,000.00, how much will its M analog go for? What would folks be willing to pay?
I am not sure.
Let's go further. Suppose they could build an M with the capabilities of the 7DII. What would people pay?
Not sure again...and let's face it, those who would buy an M at this price are NOT going double up and buy the 7DII, too, are they?
But the mirrorless thing is not going to go away.
Echoing a previous post of mine (and made on this thread by another poster), I can honestly envision APS-C, for Canon, going entirely mirrorless.
And I own the 17-55 2.8 IS Canon lens...so I've invested in APS-C as well. But there's something about the M, and mirrorless shooting, that I believe is going to appeal to young photographers, and novice photographers. It has surely caught my fancy...slow focus and all.
Sure it is too soon (even for APS-C) to say...the mirror is dead, long live the mirror. But that day is coming. Maybe not for full frame...but sooner for APS-C, I think.