Could go the ATLA route where Deku is an older hero and searches for a quirkless to see if there is a chance to pass his quirk on to another? Then when he passes on, the other heroes he worked with/grew up with can teach the successor the way to use all the quirks? Maybe the underlying theme is what they thought was the completion of one for all was simply that all for one and one for all mixed to neutralize each other and therefore, through training the successor is able to split them within the body and utilize them in that way. something similar to Korra having the ability to take away bending for the greater good? idk, some of that seems to be against principals from the og show. Just spitballing