Good question. One thing I notice with some EVF fans (not all I would add)
It appears they want every camera to be EVF, and that alone. Choice?
I like choice! No problem with EVF, but dump the OVF not a great idea.
We've already seem makers abandon viewfinders on most compacts, that's a shame, because in some situations (bright light), the back lcd is near unusable in many cases.
I think it will be hard to match a good pentaprism viewfinder for low light, the gain up of the EVF makes for a rather grainy and noisy image, with limited DR and crushed shadows, not a great choice at the moment, sure 10 years from now, it will be better. But EVF has a few problems of it's own, power drain is much higher, it's a lot more than just resolution on it's own.
OVF has issues, mirror slap (well MLU helps), % coverage, on the best models have 100%. I doubt many experienced photographers need WYSIWYG.