The wording here is interesting. It suggests that we shouldn't expect fast aperture big whites for RF any time soon.
It begs the question, should we expect this at all, or will Canon rely on the (very good performing) EF-RF adapter to allow people to use big whites on any future RF camera? It does kinda make sense to not shut out people using DSLRs from using new big whites, as the 1DX MkIII just came out, and I think it's been said in the past that telephotos have little to gain from the shorter RF flange distance.
I guess at least it wouldn't be hard or cost a lot of development money to take a big white design intended for EF, just make it a little longer in the rear, and release a native RF version as well.