A prequel involving Roshi's early years would interest me if it was prime writing it. Honestly I don't wish for anything now after seeing how poor Super has been.
I want to see what goes on in the other universes. I'm tired of Goku and Vegeta with the usual "bad guy arrives, current power/transformation isn't enough, train, get new shit, beat bad guy by some luck" routine. What goes on without the U7 Saiyans clogging the spotlight?
Probably a prequel focusing on some of the Earthling characters and their history, particularly Yamcha with how he was so savvy on multiple advanced martial arts trivia or one exploring Tenshinhan's background and meeting Chaozu. Perhaps also a Mr. Satan spinoff showing a more serious side to him in his journey to become the world champion.
That, or a war drama/space opera centred on a regular soldier in Freeza's army, exploring how the average soldier was treat and what benefits there were beyond Freeza not killing them. Some kind of spinoff exploring the Makai would be cool as long as it's entirely divorced from Heroes.
One about their descendants, though I'm pretty sure that Goku/Vegeta would somehow come back from the dead and the show would become all about them once more.
Off the top of my head? I think it would be cool if there was a prequel of Muten Roshi training Gohan and Gyumao. A pre-Cold Saiyan series could be cool too. Maybe something with Yamucha that focuses on smaller tier villains, baseball, etc.