AJA CION is probably chasing the Arri Amira segment of the market. If the footage is anything like the Amira then they may make a big splash with a first camera. The advantage is that this baby could pump out 4K. These are big mama ENG type cameras so for docu and TV work they are ideally suited. I am not entirely sure this would appeal to UW shooters as there are more options out there and smaller form factor. Cheaper too.
Having customised a housing for the Arri Alexa and the Phantom flex 4K the bulk and weight for transporting will be real put off.
The Pany GH4 and Shogun recorder is definitely looking quite good for UW. The other is KineMini 4K. This and next year will be a great tinkering time for me.
This is just my opinion. There are definitely other choices.