I think it's interesting that the third party lens makers haven't found a way to undercut Canon and Nikon (and now, with a couple lenses, Sony) on the super-telephotos. I've owned a few copies of Sigma's 500mm f/4, and it's nice for the money, but was a little less sharp than Canon's 500 f/4, and - what killed it for me - didn't take teleconverters nearly as well.
I shot primarily Sony for one year, eventually acquiring their 600 f/4, which is the close equivalent of the EF 600 III/RF 600.
I would have thought that we'd see a $8000 600mm f/4 from Tamron or Sigma eventually, but that didn't happen. Perhaps my gut impression that there must be a lot of profit margin in a $13k lens is incorrect.
As to the discussion above about Canon hurting itself with pricing, I do think that there is a segment of people not so much leaving Canon because of lens prices, but that there are people who *would* come to Canon but are factoring lens prices when deciding. Canon may well decide these are precisely the lower-margin customers they can do without.
But Canon is stating explicitly that it wants to become #1 in mirrorless worldwide. That perhaps suggests they'll do what they did with the EF range, and split it into high-end and low-end ranges, with a profusion of new "cheap and cheerful" bodies and lenses.*
-tig
*Somebody, inevitably, is going to take this as meaning the M mount will come back. No. Stop. You have your whole life ahead of you. It's just a mount.