I agree that it's very likely to happen, although I'm not sure we're there yet. The VF-4 EVF does finally have what I would call a 'barely-acceptable' resolution, but I think 4K resolution EVFs will be required to really equal the detail someone with good eyesight can see through a good optical viewfinder.
The other issue I've had with all EVFs I've tried (which doesn't include the VF-4) is the input lag is, although small, quite noticeable. Until that's fixed, EVFs are very unlikely to replace optical viewfinders for sports and wildlife photographers.
Similarly, it's hard to beat the speed of the phase-detect autofocus in professional bodies at the moment. Again, that's fixable, probably with a combination of better on-sensor phase detection and more advanced algorithms to mix phase-detect and contrast-detect data together, but I think we're still at least two generations away from a system that can accurately track a fast-moving and erratic object.
Once those issues are resolved though, I can very quickly see the DSLR losing significant market share. There's simply too many advantages to mirrorless cameras -- no heavy, soft, expensive retrofocus wide-angle lenses, no calibration issues between the focus module and the image sensor, no heavy mirror to flip out of the way for every shot, full exposure simulation through the viewfinder (and a host of useful overlays), etc. etc.
Some photographers, of course, don't need focus tracking, and can probably put up with a less-than-stellar viewfinder resolution, which is why a lot of landscape photographers (who also often don't need a narrow depth of field) are already moving towards mirrorless, at least as a second camera.
Personally, apart from the investment I have in SLR glass, I am looking forward to the advantages that mirrorless cameras will bring in a few years time.