"We have also been told that Canon will announce at least one DO super-telephoto prime lens for the RF mount. There is a possibility of two being announced. Expect slower aperture lenses, since Canon already has the amazing big white lenses that are easily adapted to the RF mount."
I wonder if any RF owners buying new big whites to use with an adapter? Adapters are great for:
1. lenses you own, and
2. used bargains, and for
3. lenses that are essential and unavailable now in RF.
My own strong opinion is that spending $10,000+ on a lens only to put it on an adapter that adds wobble, inconvenience, and is a visual mismatch is not as appealing as awaiting a lens designed for the camera.
My prediction is that if Canon wants to sell (m)any new lenses to owners of (only) RF bodies, they need to be offered in an RF mount. It's technically trivial to create a second version of any existing EF mount lens like the wonderful 400mm f2.8 IS III. Change one mechanical part and lengthen a few flex circuits. It's also feasible to sell one version with an adapter built on that can be de-mated for EF users, but is solid and a visual match for RF buyers. And the optical designers may well be able to improve performance, weight, size, or cost by designing specifically for the RF mount, although I suspect that that kind of R&D investment in big whites won't be a priority as long as EF sales dominate.
Suggestion/prediction #1: New EF big whites can be offered with a "free" adapter styled to actually match the lens. Possibly with a detachment button requiring more deliberate action for removal.
Suggestion/prediction #2: When the mirrorless tide hits the sideline pros, Canon can offer big white conversions: Maybe $3-500 for a solid bolt-on adapter that replaces the rear bayonet and adds a control ring, or $700-1000 for a replacement rear housing.
Suggestion/prediction #3: All RF TCs can be offered in a lengthened TC+EF/RF adapter form. Three bayonet connection is too many for a $10,000 lens on a $4000 body.
Personally, if I believe they're planning a RF400 DO f4 (or 300 f2.8) lens weighing no more than 2kg I might well skip the 100-500 and let the prime and TCs anchor my long end above the RF70-200.
I may not be typical in my cringing at the adapters in this context. Is any RF-only owner buying new EF big whites?