I don't think we're going to see any M-mount "higher quality" L-like lenses or physically larger lenses that are larger for the purpose of wider apertures. As others have stated, I just don't think that's the intended market for this series of cameras.
I absolutely love my M6, and I'm probably one of their two target markets:
Market 1: Photographers like me who already have full-frame or 90D / 7D size-bodies and lenses, who are looking to stay in the Canon family but want to get into the mirrorless game for the compact size and "every day usability". The small size of my M6 makes it perfect for casual travel photography, family events, etc. I love carrying it around compared to my 5D series cameras. The image quality is great *for the size of the camera and lenses*, obviously not quite up to par as you'd get with a full-frame setup, but certainly good enough for its intended purpose. If image quality is my #1 priority over all else (including portability) then I'll use my 5D and L lenses. But for everything else, the M6 serves me great. I just returned yesterday from Asheville, NC for a family vacation, some landscape / mountain photography, and it was my first-ever trip without my full-frame setup and lenses. It was awesome, and so much more convenient than carrying around a full-frame with 24-70mm F2.8, 70-200mm F4, etc. I have the M-mount 15-45mm, 22mm pancake, 32mm F1.4, and 55-200mm. There's was nothing I couldn't capture with that setup, where I said "man, I wish I had XYZ lens or aperture". At home, I might occasionally throw on my nifty-50 1.8 with the adapter for a compact portrait setup (though I like shooting portraits with the 32mm F1.4. The image quality is awesome).
Market 2: Casual photographers who have never owned an interchangeable lens camera. Even though the Rebel series is pretty small, they're still much more daunting than the look and feel of an M6 or M200. These photographers are looking for super-compact, and are shooting the same types of things I mentioned above. They have no need for capabilities above and beyond what the current lens lineup provides. They shoot for social media, YouTube and vlogs, and maybe the occasional medium-sized print.
Are there people out there that could and would use higher-quality faster M-mount glass? Of course. Is there a huge market for that on M-series bodies? I wouldn't think so. I'd venture to guess that 75%+ of the purchasers of these cameras fit loosely into one of those two categories above.
Canon is going here for the best-possible image quality that can be achieved in the smallest package. It's a balancing act. I think they've done a great job with it, and I look forward to many years shooting my M-series alongside my full-frame equipment.
Completely unrelated, I'm waiting on a Canon G9 X Mark III. I come from the old S90 / S100 + family of jeans-pocket cameras. I've never owned a G9 series, but I'm definitely getting the next one!