So here's an idea I've been mulling over for a while...
There are already 3rd party manufacturers (SigRoKina etc), who make 3rd Party lenses with AF, they take a few Canon lenses and bodies apart, look at the electrical signals going back and forth, and then build that capability into their own lenses. It's worked for the last 30 years or so quite nicely.
If only that were true!
Sigma EOS compatible lenses made before the Canon Rebel DSLR will not finction on a modern Canon DSLR. They fixed the design and reworked some of them for the Digital Rebel, then when the Canon 10D came out, some of them broke yet again. Their lenses made in the last 9-10 years still work ok. They have also had to redo some of their Sony compatible lenses that stopped working when Sony released a new model. The other manufacturers have had issues as well, but not with millions of lenses like Sigma.
Tons of Quantaray lenses made by Sigma will not work on modern Canon DSLRs even though they were supposed to be EOS compatible. I got caught with several Sigma lenses, only one could be upgraded, and they charged me $100 to make it work like it was supposed to.
Its still possible, likely even, that a tweak to Canons AF system will once again render all of Sigma's lenses non workable.
Developing a new camera is a huge cost. Some think that they just bolt parts togather with little or no effort. In actuality, its a huge effort, the software alone is super expensive to develop and maintain. A program like that can bankrupt a company, which is why Sigma bought Foevon. Pentax is tetering as well, and may stop making P&S bodies.
Don't expect Sigma to come out with a FF mirrorless, the risk at this point in time is too high.