This presumes humanity is a space fairing or interplanetary civilization.
How would something like the fediverse, internet, cryptocurrency, etc function with major latency? As an example, a signal takes between 5 and 20 minutes to travel from earth to mars. A roundtrip response would take at best 10 minutes and at worst 40 minutes. Now lets say you live on mars and your home lemmy instance is mars.social. You want to see what news people are chatting about on earth and heard that [email protected] is a good community. If you put that into your instance search box on mars.social the absolute best you can hope for is a response in 10 minutes. I assume the request would totally fail anyway due to rtt being set to low and the packets expiring before they ever reached the destination. The internet we all know and love is totally intolerant of high latency. Just ask people who use satellite internet or tor.
Edit: i think, but am not certain, that ipv6 replaced rtt with hop count. If so this may not be an issue as the time it takes would not matter as long as the hop limit was not reached.
But how would the cached copy be started to begin with? Take a server to earth and plug it in to the net? Rsync (if it will establish the connection to begin with)?
You would obviously need to adjust a lot of software that has expectations for timeouts but there is no general technical issue that would prevent most protocols from working even with much higher latencies.
The ones most affected would be the ones where a user expects interactive feedback but the computers don’t care if they have to wait 3 ms or 30 minutes for a response as long as the timeouts are adjusted accordingly.
You would have to start adjusting for that on the lowest levels though since even TCP has a lot of assumptions for reasonable response times built in.