[Irish Wolf]

A way to shrink the hyperspace "envelope" of a ship, so it can pass more closely to a gravitational point source without being forced into normal space (very useful for military and smugglers, as well as that mission to the galactic core you mentioned). It's not a "game-changer" per se, as its applicability outside the smuggling and scientific fields is limited (you can still stop significant portions of a military fleet with a gravitational interdict - this would be primarily useful for single craft).

Refinement of ship's sensors so you can scan for specific life forms, along the lines of the sensors in Star Trek. (At least, I've never seen this capability in any of the resources I've watched or read...)

Guard rails - a technology that was not mastered as of The Last Jedi.