Consensus seems to be that it would be difficult for them to pull off, but this type of thing could be devastating for worldwide internet services in the future.
The internet's decentralized nature helps a lot to mitigate this risk, but this type of attack could hypothetically even hasten the switch to satellite-based services ala Starlink.
Starlink just doesn’t have the bandwidth. There was an article about a company renting 25% of a single fiber pair between NYC, DUB and LON and it was 5Tb/s. For 25%! Of one pair! Usually there is 8 or 12 pairs (iirc) in those cables, so that’s 160-240Tb/s for that SINGLE cable! https://www.siliconrepublic.com/comms/aqua-comms-transatlant...