The Canon 6D Mk III would satisfy the hobbyist photographers that the series was designed for.
Canon has proven that they’re capable of creating great mirrorless cameras. They’ve also said there will be no more EF lenses made unless there was a specific and high enough demand for them. But that obviously hasn’t stopped third party lens manufacturers. I also think the Canon DSLR deserves one last hurrah. This would be perfectly immortalized in the Canon 6D Mk III. And just think: Canon would basically take existing technologies that they’ve had for years and recycle them enough to not cannibalize their other products. If it ever came to be, the Canon 6D Mk III would possibly be a final hit for all DSLR lovers.
Through the Canon EOS R, Canon EOS R5, Canon EOS R6, and the Canon EOS RP the company has created a full line of mirrorless full frame cameras. Parts of one or two of them could be use to create a final 6D iteration. While I’m not quite sure it should have IBIS, it could totally use one of the current sensors. The one in the Canon EOS R6 or the Canon EOS RP would work fine. Heck, the one in the Canon EOS R is the sensor in the latest Canon 5D camera. Why not just use that? It’s a pretty good sensor!
This camera would have pretty much every other body aspect of the Canon 6D Mk II. It wouldn’t need much more unless they wanted to recycle an old Canon 5D body of some sort. The 6D lineup was always well weather sealed and they were just very good cameras overall. If you needed a backup DSLR, a 6D is a great choice. If you wanted to shoot astrophotography, the Canon 6D Mk III could probably be a great option. Canon could even make the Canon 6D Mk III A for astro shooters.
Beyond this, it would make sense for them to take some other tech inside of their 1DX lineup of cameras and bring it down to this level of camera. It wouldn’t cannibalize sales, but instead would be a great way to send off the DSLR lineup of cameras. To really make it sell, Canon should offer it at low price point. They got the Canon EOS RP to a very low price point and the Canon EOS R isn’t that high either. Canon’s final 6D and DSLR camera should be pretty affordable to drive sales of both the camera and the lenses. Then after that, wish it goodbye. The EF mount has done a great job for them for years but it’s obviously time that the RF mount shines. And indeed, it can. It’s very possible for it to do so with all the tech Canon puts into it.
Most of all, Canon should prioritize the viewfinder experience. I’d be so bold as to suggest they bring back the technology from the film days where you could look at an autofocus point and it would be selected. But if not, then make this viewfinder, big, bright and beautiful the way that medium format, Pentax, the Sony a900 or the final Olympus DSLRs were. This is of course a very big experience with using the camera.
Think about it, Canon. In a time where COVID 19 sees no real end, it’s probably not too difficult to get done.