I suppose the issue is no matter how small and cheap the repeaters get, they will still need power, backups, replacements and all the complexity that implies.

I suppose the issue is no matter how small and cheap the repeaters get, they will still need power, backups, replacements and all the complexity that implies. I also have a feeling I've read the power needed for the repeaters generates magnetic fields that attract sharks. Shark bites are a not entirely trivial source of fiber cuts, which require very expensive fleets of cable repair ships to be maintained on standby and simply driving down the number of fiber cuts could be a fairly significant source of cost savings.