I started looking more closely at an upgrade from my GH5M2 as I do not like the GH6 housing so I though maybe take the opportunity for a rehaul
As of today there are only three Sony cameras that support this and one planned. I prefer Sony as they have more options for wet lenses
1. A7 IV _> Super35 crop
2. A1 -> full sensor pixel binning
3. A7S3 -> full sensor
4. A7RV -> Super35 crop
The A7 IV and A7RV have shocking rolling shutter in full sensor readout and only really work in Super35 mode properly.
This means the only real option are the A1 and A7S3. If you want to also use the camera for photos only the A1
I then looked at Canon there are 3 models
1. R5/R5C -> 8k
2. R6 MkII -> 4k
3. R3 -> grip style
Here the R5 is the only real option as the other have rolling shutter or are grip style (I do not want a grip camera). The measured performance of this camera is not better than my current camera in Video (!) however there is good noise reduction in camera
Support for wet lenses is lower with WACP style option but you can reuse EF lenses.
Verdict interesting for photo OR video upgrade but not for both
Nikon
1. Z7 II -> pixel skipping (not binning)
2. Z6 II -> Super35
3. Z9 -> OK
Again not interested in the Z9 form factor.
This is the reason why I concluded that the only camera that offers an upgrade path to both photos and videos is the Sony A1 unless you want a grip style camera
If instead you are only interested in video and don't need 8K again the A7S3 is the best option
The A7S3 costs 2.81x the GH5M2 to only improve in video. At that point I wonder if the GH6 is a better path as I can use the other lenses and ports but the A7S3 housing is cheaper and the 28-60mm lens is also cheap but if you start with other larger optics this snowballs. Yes I would say starting from zero the A7S3 does offer all options in terms of performance
The A1 costs 4.82x the GH5M2 and improves on both camps however if you look at starting from scratch the ratio camera + housing becomes 9,916/5791=1.71
Obviously lenses for full frame are more expensive but not a great deal ports are bigger and more expensive but I have already made that step
I guess my conclusion is if money no object and you are not invested heavily in MFT A1 is a path you can follow especially if you are only interested in underwater.
If you are already a GH5 user with the housing the easiest option is to get a GH5M2 or a GH5S depending on what you look for it then becomes very costly to switch
I will be reflecting on the A1 until Xmas and potentially rent the camera to check a few topside scenarios