Librarian enchanted book trade suggestion

Instead of librarians unlocking random enchanted books, how about you have to teach them an enchanted book by supplying them with one before they unlock that trade. So for example if you want a mending book trade from a librarian, you would have to find one first in the world through exploring or fishing, then give that book to a librarian to allow him to unlock that trade. This would remove the incredibly tedious task of re-rolling librarians and force you to explore or use the enchanting table more. This could also fix a shortage of special books like swift sneak on multiplayer servers if that was also added to librarian trades.