But even the massively expensive 1DX III can't do eye AF in the OVF, not to mention Animal eye AF. And it doesn't cover 100% of the image either. That's not a restriction of the size of that sensor, as far as I know. It's an problem with the amount and angle of the light hitting the AF sensor. And that's despite how complex of a design it is (it's unlike what's found in any other Canon DSLR). Sure, if you throw enough money at the problem, you can match the R5 performance with an OVF - but probably not at 5D series prices.Improved Autofocus: the 1DX Mark III can already do face and head recognition through an *OVF* AF sensor. That in itself is rather impressive. This sensor could grow to cover a larger AF area to match the 90-100% image sensor AF coverage of mirrorless.
Not to mention IBIS, which is simply better suited to RF cameras with the faster communications in the more modern mount and the greater range of motion due to lacking the mirror box.
A DSLR will not match the features of Canons new mirrorless options without going up in price. So the options are giving the market a minor upgrade over the 5D IV, moving the 5D upmarket or simply abandoning it to not cannibalize R5 sales.