So people naturally want to know what products are going to be released in the future. Why? It influences buying decisions. Do I want to buy an iPhone 7 the day before the iPhone 8 is going to be announced? Probably not. There are sites dedicated to rumors or future products. They get their information supposedly from informed sources.
The current M line is pretty well filled out and up to date. The M100 as the entry level model, the M5 as the advanced amateur with a viewfinder, and the M6 without the viewfinder. A used M3 also works great, I have two myself and still shoot with them in addition to my M6. The current M line is not really lacking any must have feature or some new technological development. Some would argue they need 4K video, but that’s not something I personally need.
The one model that there has been speculation about is a full frame mirrorless model from Canon. This would be the next logical model in their line up. Since Nikon has announced they are working on one, Canon really needs their own too. I’d like to see the latest iteration of the 5Dn, 6Dn, and 7Dn lines in a mirrorless body with a similar feature set and image quality. The current M line is equivalent to the 80D, so a 5Dn or 6Dn would make the most sense. I’d most likely buy the 5D equivalent, though I am wondering if EF and EF-S lenses will fit on with no adaptor? I’m not concerned about fitting EF-M lenses since they wouldn’t work anyways, but will EF lenses fit? I would guess they would have to and that they won’t have an entirely new lens mount.
In Feb 2018 the Canon M50 was announced with 4k video, Digic 8, fully articulated screen, etc so Canon is clearly dedicated to the M line for the future. Moreover, Canon shifts focus from SLR to mirrorless cameras explains the company’s thinking about shifting focus more towards mirrorless and away from DSLRs since that’s the way the market is moving. Note however the M bodies are $980, $780, or $450 so price points suggest entry level and advanced amateurs. No 7Dii, 5Div, or other body of this caliber.
My guess is that a higher end APS-C M will be introduced and hopefully an entry level full frame M system at some point. The APS-C entry to advanced amateur seems to be well addressed.