Originally posted by Paul the Sunman the viewfinder would operate as an OVF when using SLR lenses and as an EVF with mirrorless lenses
Consider the source (Tony Youtube, not the OP) and then remember that there was a discussion here several months ago about exactly the same thing. I checked my posts to try to find the thread, but I can only go back to June of this year. Somehow, someone got the idea that RF mount lenses offer something that isn't available in Canon's other mounts, so Canon must be working tirelessly to find ways for those poor folk who can't afford to replace their 5D's with an EOS-R to spend money on these special RF mount lenses instead. Too bad Canon didn't fill the gaps in their existing lens lineup before they started producing these fantastic new lenses in RF-mount.
Mind you, in the real world, Canon has already produced an EF to RF adapter, so people who buy the EOS-R cameras can use the EF lenses they already own on their new cameras. Any Canon user that feels the need to use an EVF is not restricted at all in the lenses they can use to take photos. That only makes sense, this latest rehash of the how do mirrorless zealots convert DSLR devotees is just plain nuts.