We have received some information from one of our sources that has seen the camera, and described it to us. He mentioned that EF lenses mounted directly onto the camera body.
We have been told in the past, that this will have a mount with a sexy solution for EF lenses, so we're going to hypothesize a bit about what we think it just may be based upon some patent applications we have seen recently.
In this patent application, Canon describes a mount that supports two different lens protocols. This is further described in these two patent applications where they discuss switching the lens mount to support two different protocols.
From this information, it's a working theory that the RF and EF mount will differ slightly and EF lenses will mount on the RF mount and cause it to “switch” to the EF protocol. If you mount an RF lens, it will switch back to the native RF protocol to support the lens. Interestingly, this locks the RF mount up into Canon's patent portfolio which will make it difficult for third party mount adapters to support on other camera bodies.
Right now the information coming from sources is extremely vague. Canon is keeping this completely under wraps like no other release that we've seen in the past. This may be entirely conjecture, and may not actually be what Canon is doing, but at this point in time, it sounds like a plausible scenario.