So...at the risk of being a contary opinion, I'm not a huge fan of the mirrored/mirrorless categorization. I think it's too late for one thing - the micro43rds have been discussed for years in the SLR forum - and I also think that these days its a little bit of a meaningless designation. Defining a camera class not by its features and housing aspects but based on something it doesn't have??
Both SLR's and many but not all mirrorless are "single lens" designs, whether they provide viewfinding only with the rear screen or with an EVF, the 'viewfinder covers the actual sensor view' behavior is preserved. Many mirrorless also provide PDAF on lens (and the SLT's are another midway providing it but not the viewfinding with a reflection). There's no longer any meaningful sensor size distinction either with mirrorless having anywhere from sub-4:3rds (Nikon's tiny ones) up to FF sensors. For that matter there are now full frame digicams...and everyone has video.
The only major distinction these days seems to be between interchangable lens cameras, and not (oops, there's that designation-by-absence again) at least as it pertains to underwater shooting since one needs lens selection and port selection...and the other might only take wet external lenses or filters. That, and intended usage/interest, so of course having a video vs. stills forum distinction still has a lot of meaning with lights vs. strobes, and processing and all.
Seems to me that the posting frequency here at WP in general has dropped off a lot in recent years, and fragmenting too much for too little distinct difference in behavior (without cleaning up much of the history) is just confusing and ultimately not beneficial. Maybe DSLR guys didn't like all the mirrorless discussions in "their" forum (?) but I think in a few more years with on-sensor PDAF development and faster chip readouts, the true classic "DSLR" design may go the way of the film SLR in becoming a small niche, while these hybrid designs take over. Assuming cell phone cameras and POV video sets like GoPro don't just take over the whole imaging market first... heh.
Anyway I'm sure I'm in the minority on this one, but recent posting patterns despite the new forum option just made me chime in regardless. Feel free to ignore me. My wife does.
Current rig: Sony SLT-alpha55 in Ikelite housing, Sigma 105mm f2.8 DC Macro w/ Ike 5505.58 flat port or Sigma 8-16mm f/4.5-5.6 DC HSM behind UWCamStuff custom 5" mini-dome. Dual INON z240 Type IVs triggered with DS51 for TTL mimicry, or DS51 alone with home-made ringflash assy for macro.
Topside, unhoused: Sony SLT-alpha99,
Sigma 150-500mm + 1.4TC (Saving for Sony 70-400 G2), Sigma 15mm diagonal fish, Sony 24-70mm f2.8 CZ, Tamron 180mm f2.8 Macro...all the gear and nary a clue...