I'd like to have some kind of a tether harpoon with physics enabled between the ship and the tethered object. It could create extremely funny gameplay moments when both are objects of similar mass, eg a Sidewinder tethering itself to a large chunk of USS debris, which is then smacked by a boosting larger ship. I'm sure we've all played Thrust or one of its descendents here.
What would it be used for? Throwing each others' SRVs at skimmers, lifting them into orbit, grappling to asteroids to run cold, grabbing annoying authority Vipers in a RES and mashing them off asteroids, that sort of stuff.