Unless you know of some standard that uses TCP to encapsulate the entire capacity of optical links it's fine. These links are layer 1 links that are separated out and reduced substantially in capacity before they are fed to data link interfaces let alone IP or, above that, TCP. That's ignoring that these core network links handle millions of flows, they aren't being saturated by a single enormous TCP stream for obvious reasons - to do so means it's not really a core network link as it's not aggregating anything, it's point to point with some insane network cards / shelves at the edges fed by some insane servers.
Applications requiring immense throughput don't use TCP in any event.
Going forward they can either modify existing headers or populate something into the TCP options field if they need to but this is a solution looking for a problem for the foreseeable.
