A lot has happened in the time since the EF mount was launched, especially in cryptography. Unless Canon are extremely dumb they will require all RF lenses and RF->EF adaptors to be digitally signed making it pretty much impossible for anyone without NSA-level resources to reverse engineer the protocol.
Plus, there will be patents galore to deal with.
No third-party RF lenses unless Canon allow them.
They certainly have the capacity to do this. Whether it would be advisable is another question.
I know for my part that if Canon eliminates compatibility with third party lenses, then I'll be deciding between the other manufacturers. I have relied on Tamron and, particularly, Sigma to fill in holes Canon hasn't had the capacity to fill. I don't think I'd be happy limiting myself to a single manufacturer. So many of my images I'd have missed had I tried to box myself into a single camera manufacturer's system.
Indeed, the fact that RF is here and that there is tumult means that it's the time to do one's due diligence. If RF is compatible with the legacy third party EF glass and the RF mount is available for future third party development, it looks like the horse to ride - at least from this distance. We'll see when the cameras are delivered. If you take out that capability, though, Sony and the Z mount both move above.
This isn't some "stupid Canon" complaint post. I'm just pointing out that Canon is unlikely to make this move because it would suffer a loss of body share in trying to protect its lens share. And body share is where the future is, especially at the moment you opt to switch mounts on your millions of customers.