An EF to RF adapter is less of a liability than an EF 1.4X III or EF 2X III extender. Lots of 1D X Mark II shooters use extenders regularly.
Most action/sports shooters are used to using extenders without considering them a durability liability.
Many 1D X type shooters who use lenses above 300mm already frequently use extenders.
An EF to RF adapter is simpler than an extender, which has optical elements that can become misaligned.
An EF to RF adapter can be just as weather resistant as an EF extender, and has no optical glass in the light path.
It's not even really an "adapter" in the sense that a cross platform adapter has to "translate" between the camera and lens.
EF and RF lenses and bodies are both backward/forward compatible with one another.
There are no top secret protocols to reverse engineer since the RF protocol is built on top of the EF protocol and the same entity owns all of the IP for both of them.
There's only one additional connection. A lens to camera is one connection. A lens to adapter to camera is two connections.
Many professional 1D X users already use extenders in such environments. There's no real practical/functional difference other than the adapter has no optics that degrade the lens' performance.
Tripods for wildlife. For sports, you don;t very often see anything more than a monopod for the photographer's heaviest lens.
It's exactly the same as the one extra interface that many 1D X users shooting sports/action/wildlife have no trouble using with an extender. Are you saying 95% of pro sports shooters are not sane?
When you ask a sports shooter if he wants to use adapted lenses, he's thinking EF glass on a Sony α9 and the resulting reduction in frame rate from 20 fps to 5 fps. There is no such penalty for using an EF to RF adapter between EOS lenses and EOS cameras.
The 20µm number came from
a post by Uncle Roger (scroll down to the section under "Camera body variation also occurs). It had nothing to do with AF. He was discussing perceived blur from one side of the frame to the other in images taken with wide aperture, wide angle lenses. He also made clear the tolerance is higher for narrower angle lenses.
The reason some mirrorless systems have AFMA is to compensate for lenses that do not move the focusing elements exactly the requested distance when the camera instructs the lens to move. Making lens focus element moves more accurate allows faster autofocus because it requires fewer follow-up measurements and movements. It has absolutely nothing to do with tilt.
Most of those loaners are for accredited pros who own gear breaks during the event.
It can't.
The reason some mirrorless systems have AFMA is to compensate for lenses that do not move the focusing elements exactly the requested distance when the camera instructs the lens to move. Making lens focus element moves more accurate allows faster autofocus because it requires fewer follow-up measurements and movements. It has absolutely nothing to do with tilt.
1D-series cameras can be used with extenders under any condition as well. There's no fundamental difference between an extender and an EF to RF adapter except no addition glass.
There are no aberrations that will make the captured image blurry at the same spot on the sensor that it was sharp during AF, because the
same exact surface that was used to focus is also used to capture the image. AFMA in mirrorless cameras is to compensate for errors in focus element movement so fewer follow-up measurements/movements are needed.