Make humans great again
Been pondering ways to do this.
Remember when Tien demonstrated an ability to not only copy techniques after seeing them once, but also improve them? What if he did this with Kaioken.
Say, it brings him up to a level where he can keep up with SSG, and an improve Kikoho lets him punch above his weight class, at the cost of his health?
Lets face it: short of giving Goku some advice here and there, and/or lending him energy, humans will likely never play any kind of significant role in the story again.
Hell, aside from Roshi during the ToP, humans haven't really been used in any kind of overly significant capacity since early in the original DB story -- back when Goku was still a kid and weak enough for humans to contend with. Sure, humans have had moments to shine here and there(most notably Krillin during the Freeza saga), but it has been an extremely rare occurrence.