Reading through the comment tree, I'd say general consensus is that, in the case of a long distance underwater cable, link encryption is technically feasible.

Reading through the comment tree, I'd say general consensus is that, in the case of a long distance underwater cable, link encryption is technically feasible. However, while technically feasible (so as to protect metadata, who's talking to whom, etc.), due to the political weight & financial heft of certain state actors, tapping at the cable link endpoints would remain a strong possibility. This would obviate the actual need to link encrypt except of course for "optics"/marketing to data center customers.