I'm not a networking expert, but imo i think that with extreme delays, you would not want a real-time transport medium at all. The higher-level protocols would be built on top of a non-real time substrate. You would want to have so much forward error-correction that you could remove ACK completely (perhaps a higher level protocol could still be used to request retransmission in the rare case of failure, e.g. one could request a web page be resent via HTTP, but the hypothetical TCP replacement under that would have no concept of ACK).