I think it'd be cool to be able to fast travel between the seaposts. Right now it often feels like the map is quite large, especially in a sloop. If I want to grind ashen Athena and I spawn in the Shores of Plenty, I typically re-crew for a different outpost.
I guess I picture a teleport system that works kinda like a moba recall, to prevent it from being used for running, or for short distances. Have a big obvious indicator like that for tunnels of the damned, and make the teleport ritual take 3 minutes or so. If the ship gets damaged in the slightest, the ritual would be interrupted and crews would have to retry.
Overall I think it would shrink the map significantly, and give more use to seaposts.