===And how, harry, is an EF mount camera going to control focus or aperture on an RF mount lens? You can't even manually focus the lens without electronic control from the camera.
Don't be so daft. There won't be any adaptors for RF to EF. It's about as likely to hit the market as your magic codec.
I highly doubt Canon itself will make an RF to EF adapter...BUT... I do think someone like Wooden Camera might sell one as a package along with one of their Camera Cages and/or other accessories. In terms of focus and iris, they could put a control ring into the adapter itself for semi-automatic and full-automatic focus and iris control protocols which already have been reverse engineered from a technical point of view by Sigma and others.
The key issue is simply the ASTOUNDING QUALITY of the new Canon RF mount F/1.2 50mm lens! Any accessory manufacturer who can make an RF to EF/EF-S adapter at around $275 to $350 U.S., even IF it uses Acrylic corrective lens elements, WILL sell a bundle of them to all the VLOGGERS and prosumers who've got a ton of Full Frame Canon M50's and 5D's and ASP-C 7D and 6D cameras wanting to extend the lifespan of their cameras with higher end lenses that can TRANSITION to newer RF cameras once their old cameras finally die! This is a market EAGERLY WAITING to be served!
In fact, I expect within 6 months the first of RF-to-EF and RF-to-EF-S adapters to be coming out! Will they have separate control rings for BOTH iris and focus, AND ALSO neutral density filter holders or a turn-dial-form neutral density selector built-in? THEY SHOULD but we shall see what comes out and at what price point! The magic number for willing buyers SEEMS to be between $275 to $350 U.S.
I have to give Canon kudos, no matter what esle is coming out in the near future from others, I do must say that their first set of new lenses are UTTERLY SPECTACULAR and DESERVES every accolade given! So start on the truly high end RF mount 400mm 600mm, 800mm and 1200mm lenses! AND a super fast high end F/3.4-F/5 150mm-to-600mm or so SPORTS ACTION WILDLIFE zoom lens!