I keep hearing all this talk that “mirrorless cameras will completely replace DSLRs” or the like. I don’t buy it. Often it will be with a statement like “this camera is smaller and lighter and meets a pro photographer’s needs.” Yeah, sure.
First, let’s talk about viewfinders. All mirrorless systems, with the exception of the Fuji X-Pro1, use the sensor to beam the preview image to either a screen or an EVF. That works great and is working better with each new iteration. The problem then? Optical viewfinders still work better, look better, etc. Yes, it is nice having a visual exposure preview, but I don’t think it’s worth the exchange. There’s another aspect to this too. When you’re using the sensor constantly for the preview image, you’re heating it up which will reduce your image quality. No issue with that while using an optical viewfinder, so you will get cleaner images, all else equal.
Autofocus is still better when using a dedicated system like in a DSLR. Mirrorless systems are doing quite well though. Most are perfectly good enough for most situations, but I know of none that could pull off a good focus in extreme low light like the 6D with its -3ev sensitivity.
How about the sensor itself then. I’m pretty sure it will change eventually, but there are currently zero full frame mirrorless cameras. Yes companies are doing very cool stuff with sensor technology in these systems, but remember they can do the same cool stuff with bigger sensors too. A bigger sensor is (almost) always better, and “big” sensors are advancing just as much as “little” sensors.
I could see certain CSCs being used heavily for some branches of photography, but I don’t think they’ll ever completely take over. I don’t see the H6D being a mirrorless compact.