That would create a DSLR that performs much better in live view mode than when it is used with the OVF. There is no point in such a camera, if you don't use the OVF any more. View finder type and AF type are tightly coupled.I wouldn't understand why Canon wouldn't release a 5D Mark V.
90% of the job is done.
Body and shape : just re-use the Mark IV, it's perfect
Sensor and DIGIC : just re-use the R5
AF : just re-use the AF of the 1D X III or a "lighter" version of it
I'd gladly buy such a camera. Throw at it something unique such as a feature to get rid of this AF micro-adjustment thingy and it's a dream come true.
Mirrorless cameras will easily supersede DSLRs, when both, AF performance and view finders are superior. Does the R5 mark the tipping point here? Maybe! We will see very soon.