This post will be a bit surprising for those that think I am an MFT partisan and despise any other format, as you probably imagine that is far from truth. This post will look at the strength of the APSC DSLR segment.
If you follow the rumours and announcements of Canon and Nikon you are probably aware that Nikon is not planning any new professional APSC DSLR and Canon just released the last model with the 90D and will not be releasing a new 5D camera having just released the 1DX Mark III.
This is going to be a significant blow to underwater photographers around the world as today most of competition winners shoot an APSC DSLR camera, in particular the Nikon D500 is probably the most popular camera of serious underwater shooters.
What makes APSC DSLR Unique for Underwater Photography?
In an image we can understand what has made this format such a great option

The Tokina zoom fisheye is simply the best native option for wide angle underwater photography. It is cost effective and despite the apparent low quality on land it takes some amazing underwater pictures.
What makes this lens even more interesting is that it produces decent results with a small 4.33″ dome.

There are several option acrylic and glass and if you want even better quality you can go for larger dimensions.
Today you can get the Tokina 10-17mm with his port for £1000 which is less than the cost of a Nauticam WWL-1 and much less than any WACP or Nikkor Nikonos vintage lenses.

Another extremely popular choice but this time for macro is the Sigma 105mm F2.8 EX DG OS HSM Macro Lens or otherwise the OEM Canon 100mm and Nikon 105mm macro lenses. Those have been taking some amazing super macro shots in the last 10 years plus thanks to 150+mm equivalent focal length.
APSC Mirrorless Cameras
Both Nikon and Canon have launched new mirrorless APSC and with that a new lens format. Sadly the Tokina 10-17mm autofocus will no longer work. This is a major blow and we need to understand if Tokina will delivery a Z mount version of their mythical lens.
Mirrorless cropped format has been the domain of Sony and Micro Four Thirds due Olympus and Panasonic for the last 5 years and it looks like there are no benefits at sensor level between 1.5, 1.6 and 2.0 crop that are meaningful.

The other issue is that Canon and Nikon mirrorless are also behind in terms of autofocus compared to MFT, while they already are matching or beating Sony.
As a new user would you buy an APSC camera from Nikon or Canon or prefer Sony? Would you just get a micro four thirds that at least has commitment from two brands and a complete set of lenses and ports for underwater use? Nikon themselves have branded their Z50 camera as a non professional unit and make self limiting design choices that are evidence that their commitment is for full frame, this is the only segment where they are making profits currently.
Future of Full Frame DSLR
Canon is definitely abandoning the DSLR ship and has some good mirrorless penetration with their 5DSR and have just announced the EOS R5 that will be the first unit with IBIS and have 8K video.
Nikon is still hanging to their upper range D series for full frame DSLR but it has been also moving strongly into full frame mirroless.
Both Canon and Nikon are no longer developing their DSLR lenses mounts.
Considering the domination of Nikon in the full frame underwater photography segment the full decline of DSLR will not happen for at least another 2 or 3 years but the time will come.
Conclusion
The extinction of APSC DSLR is not good news for underwater photography as currently no other format can match the choice of ports and lenses available to those shooters. There is a risk that a camera like a Nikon D500 becomes a precious 2nd hand commodity however shutters do wear out so this is not a sustainable path.
A few years ago we witnessed the death of compact cameras to phones and this was a first blow to entry level underwater photographers.
The upcoming death of APSC DSLR is going to hit deeper in the semipro user group however alternatives are available thought not matching the same flexibility of lenses and ports.
Our passion is getting increasingly more expensive as the digital camera market focusses on full frame and also more bulky and difficult to carry around.
I think that is possible work with Tokina 10-17 mm lens with one adapter in the Canon mirrorless APS-C M cameras.
Yes but autofocus is not supported!