It was never promised but there are several patented versions.Was it ever promised? Can you point this out for me? I can't see it ever being released personally.
It would be a very different lens than the RF 100-500 L, so both lenses could exist.
However, Canon would want to entice people into buying sets of zooms and they seem too close for that.
On the other hand, most people seem to choose either the RF 600 f/11 or the RF 800 f/11.
Very few people seem to choose both and Canon does not seem to care which one.