Make gravity generators work a bit differently. Have them give a ship gravity, instead of simply making a player on the ship feel gravity. That is, if it is on, then a player who has never been to the ship will enter its gravity automatically without needing to find a gravity block.
Of course, some form of fine-tuning the gravity may be necessary, perhaps having a new block that determines where on the ship there is gravity rather then relying only on the ship\'s \"chunk size\" (allowing for damage to knock it off-line for some of the ship, or for a zero-gravity area like a docking area to be built in). And for the sake of the physics engine, it will NOT affect other ships.
The reason they probably don\'t have plexlifters on ships right now is likely due to some iffy mechanics in making sure things on a ship (players) stay, well, ON the ship. Activating gravity can help you stay in place as a ship moves, but its still a bit alpha on account of being in alpha.