While I hope that the EF mount sticks around, the new EF 400 and 600 lenses don't confirm that. I expect RF lens development will focus on where the mount has an advantage (such as the lenses currently offered). Long RF tele primes and zooms will have little advantage over existing EF lenses with an adapter, especially the new ones where I expect the focusing algorithms and possibly drive mechanisms have been updated.
If I understand what you're saying correctly, having an EF super-tele with adapter won't be much different in practical use than having an RF super-tele. Thus, Canon anticipates the full move to RF bodies can happen just as soon as a pro body RF mount body can do what flagship DSLRs can do -- all without upsetting those who invested in EF mount super-teles? That's a fair point, I think.
My point was that whichever way Canon goes, I expect that the needs of EF super-tele owners will factor into how (and how fast) they make the full move to RF mount bodies. Whether it's EF working seamlessly on RF bodies or EF bodies persisting for another decade, EF lenses won't quickly become obsolete (like, say, when the EF mount was introduced). Does that make sense?
