The only way this makes sense to me is if there is the ability to create something akin to the cargo container as a building block of a data center, where you can have arbitrary compute and storage plug into a greater complex.
Every computer design has some element that will render a large part of the design inoperable in case of failure. Either it is a SAN head (even if you have two, the fail over can malfunction), or a switch setup.
Then there are things like failures of simultaneously purchased components (hard drives purchased at the same time, that are worked the same load will roughly fail at the time).
A custom made barge with dynamic positioning gear and a grabbing/coupling system to detach the pod from the subsea grid, lift it, and then re-attach it would make the servicing relatively efficient.
I could see the roundtrip time for a full hardware replacement of a pod being under an hour, conceivably under 10-15 minutes.
Which is something Google already did[1].