I really can't see the benefit of submerging these -- the complexity involved with keeping out several hundred PSI of sea water just doesn't seem to make sense to me. For the cooling aspect, they're already using pumped water and heat exchangers. What is the benefit of submersion vs just pumping sea water from a pipe to a land, or barge-based datacenter and using that to cool?
Why does it have to be several hundred PSI? They don't have to put it at the bottom of the ocean. A shallow lake or river would work just as well.
50msw = 74psi
200msw = 293psi