My 2 cents --
I know many are hot to trot on mirrorless, but, I think its more of a fad than a lasting viable system. The biggest problem is glass - not enough native M mount glass out there. In my eyes, the logical solution is to figure out a native mount that accepts EF glass (for canon at least, whats the designation for nikon, DX?). And that's where things get tricky for mirrorless - using current EF glass means that many of the advantages (size, weight being the biggest) of mirrorless are lost. So your stuck in the rock in the hard place - buying a mirrorless for size and weight advantage then having to choose between excellent IQ (EF glass, but that kills the size/weight advantage), or subpar IQ (using smaller, lighter M glass, keeps it small and lightweight but at the expense of IQ), or using an adapter to use EF glass, which will hurt IQ even more.
I kind only see mirrorless working as nothing more than a consumer option. What they should to is actually find a way to remove the LCD, and replace it with a dock for a phone (hard to do because ports are not standard on phones, so you'd have to create a camera for each phone mount). Now that would be the way to combine the 2...alas though it will be wifi and wifi only for that. I read thought this though and see all the little things people want, touch screens and the like ----its grasping at straws because in reality you just want your phone to take nicer shots. and I think that will be the final nail in the mirrorless coffin --- the market that mirrorless appeals to is the market that will say, I don't want to carry 2 things when i can carry 1, afterall, can I play candy crush on the camera? Can this camera slip into my pocket? Nope, you'll need a bag for it. Lenses? You'll need a larger bag unless you want a jack of all trades 12mm-300mm f5.6 compact lens (yeah, there isn't one yet, but to be viable, it would have to be tiny and light which means a trade of of size and weight for less IQ).
And as for potential pro use - I look to what nikon and canon are doing with their glass. high end glass is made for DSLR's - and it doesn't look like either company is breaking that trend. Without high end glass this won't be a pro option. I know sony says they have a lens road map for their A series, but, this is sony we're talking about here so they may have all the glass ready by the time the next fad has arrived, and sony likes the fads...
So again, I think mirrorless will be a fad unless they can make native mounts for existing glass systems - and even then it will only take off if there is some kind of very real tangible benefit over a DSLR. I watched that kai video, and it astounded me that for some reason the mirrorless A7 and A7r are louder than my either my 5d3 or my 6d on silent mode ---- WHY?
? why in the world would they do that - for nostalgic purposes? I don't get it at all. why make a loud psuedo shutter clack if the main benefit is that there is no shutter to clack?
?? And this gets me to my final point --- take away the weight and size benefit, and what is the real advantage? it's mirrorless so the burst rate should be off the charts --- nope...5 fps on the A7, and 4 on the A7r. No shutter, that should lead to higher x-sync speeds right --- nope, 1/160th and 1/250th. Seems a lot like what we have in a dslr right now.
How much do many of use here have invested in our current system? Think on that. then consider that there really isn't anything mind blowing about mirrorless (IE, there is to my knowledge absolutely nothing that can be done with a mirrorless body that you can't do with a DSLR), why would we sell of the gear to switch? We may buy one as a novelty, use it for a few months then add it to the shelf of things collecting dust. Again, there is nothing mindblowing because the tech inside camera's has hit an apex for now and we all have to wait for the next round of big advances in other tech areas before we see another round of mind blowing advances - mirrorless is adopting this because there's really not much new stuff they can do.
the future of DSLR's:
As said in that last statement above, I do foresee a longer shelf life for models. i like the idea of the buyback program, as time goes on that will be a big factor. I'm not sold on the idea of sending your camera in for an upgrade to the existing body --- my guess is it will be a loyalty kind of thing --- a trade in (IE buy the 5d4 new at $4k, or trade in your mk3 for a mk4 for 2K. HAHA, there's that mirror...if your going on 3 years with your mk3 changing out the snesor and processor would be great, but that mirror will need to be replaced too.
And before I get flamed for all of the above...these are just guesses, and I am probably wrong....lol