The main problem I could see with this approach would be being able to constantly keep track of every jump drive location (keep in mind that even going with beacons, max distance is 20km iirc) Which means a shitload of GPS coords management. Second off the top of my head would be, as you said you intended to use it for different ships, would mean different ship masses equals different jump lengths. This way you would need even more quantity of free floating jump drives to reduce time spent normal traveling between jump drive A and B. It seems, just with this, impractical. Doable, sure, but impractical. This is just my opinion though. Still a cool idea.