Of course it would work well. But it also comes with downsides, such as the AF in an OVF always working with just a fraction of the light coming through the lens (the rest goes into the user's eye) and just the massive cost associated with an additional sensor of such complexity.Yep. Just imagine had Canon dumped their R&D dollars into developing that tech. I really suspect it could have rivaled what we are seeing with mirrorless. Maybe even surpassed it as each sensor could be optimized to a specific purpose.
We are pretty sure there won't be a 5D V, but a 1DX IV might still come around one day for those willing to pay the premium for using such an extravagant AF setup for the purpose of coming close to mirrorless performance with an OVF.