Power it with offshore windmills, and you really only need a network connection.
Great idea though, using water to cool your datacenter and leaving all the oxygen out.
The MSFT Datacenter is a vessel under law, if they don’t want to fly it under a flag they’ll have to essentially abandon it and then salvage laws come into play.
In a more fun world, one of those vessels would fly the Jolly Rogers and host a certain infamous Swedish bay.
As for “without laws” google still follows European laws even if my search happens to be handled on an American or British machine. You obey the laws where you operate not where your server is located.
But if the economics in the future make sense on some level, I could see criminal enterprises interested in exploring things like this. If narco's are building/using submarines now, I could see them managing/tracking/monitoring a global logistics from their sunken data centers (they'll need to find other ways to power and transmit/receive, because I doubt they could just hook up their cables directly onshore anywhere, setting aside being an easy choke-point to cut access).
Maybe future narcos, illegal EU personal data miners/brokers, pirates or who else for whatever could be interested, esp if the fixed cost of operating stuff now/future > operating/ future sunken data centers and probability/cost of seizure now/future > probability/cost with future sunken datacenters?
For example: industrial, unregulated fishing destroys coral reefs every day. They are thousands of years old and won't come back.