Great summary and nothing like pictures to see the size differences with your own eyes.
Seems like it is a good time to be a consumer since we have many quality choices.
I was shooting a compact camera for UW video. Canon 7d DSLR APS-C topside for photo & video. I wanted something better for UW and I wanted full frame for topside. I considered a GH4 and a Canon FF DSLR, but that meant 2 new cameras. Along comes the Sony A7s ii. Wow, I achieve both goals with 1 camera.
I think you are right that DSLR will take a hit. People like to keep their lenses and upgrade their camera bodies. DSLR owners now have the option of doing that with mirrorless.
the size of the camera is not the problem.
But the weight of the housing...
Nauticam for a6300 will not be much more than for the a6000 and that was ~ 1kg!
Nauticam housing for the A7 series 2,4kg......
And the lenses......
If i want it big and heavy, i would take a dslr.
Last february in Malapascua for tresher sharks, the oly was simple not fast enough, or the iso is not usably with mor then 640.......
Thats the reason for my to change!
Thanks, now I understand. I can see mirrorless FF and APS-C putting a big dent on 4/3. Bigger lens choice and existing DSLR owners can keep their lenses. Size is always a factor. FF low light capabilities, plus being able to switch to APS-C mode in camera are huge benefits.