Nah, social media is plenty feasible and the Twitter UI/abstraction is probably ideal like GP says (although I think the implementation would be different than you're imagining.) They'd just colocate on the other planets and replicate the database. Stuff like that is a solved problem (in the case of TCP, just increase the window size. Although you'd probably want to make sure transaction boundaries and packet boundaries line up to minimize latency/jitter. If they wanted to minimize the latency they'd make large media available as a merkle tree and make blocks available as they arrived correctly a la Bittorent or IPFS (heh.))

The delay this introduced would have a social effect similar to time zones: "Oh the martians are caught up to event <x> and their reaction is <y>" instead of "Oh the Australians are waking up after event <x> happened today and their reaction is <y>."