Isn't simple distance scale ( like a split prism
) much reliable and easier to implement. For me the hardest part about AF confirm is guessing when the dot is about to appear and slowing down.
Usually i end up iteratively approaching it from both directions...a scale would cut most of those steps leaving some 2..3 fine adjustments.
Well there are many such inexpensive, simple things like this which for various reasons are never implemented.
But if they figured how to make non blanking OPTICAL TTL viewfinder system with sensor continuously available to exposure would be nice.