My prediction for cast is built around story mode. I expect a Guilty Gear like story mode, based on manga, possibly starting at saiyan saga and ending at Golden Frieza. If they do an original story then throw my post out lol.
Cast will not be too obvious and needs diverse fighting mechanics since dev said the 6 revealed characters are the more standard ones. So i got Babidi, Bulma, Roshi, Nappa, Recoome in there. Another factor on cast is how sellable DLC could be while leaving room for sequel.
*Main Heroes
Goku
Vegeta
Kuririn
Piccolo
Master Roshi (Technique user like Mafuba, getting swole, etc)
Bulma (uses tech)
*Saiyan/Frieza Arc (In story you fight vegeta)
Nappa (grappler)
Recoome (grappler)
Ginyu
Frieza
*Android saga
18
Perfect Cell
Teen Gohan
Future Trunks (uses sword)
Mr. Satan (fun, joke attacks)
*Buu Saga (in story you fight Majin Vegeta)
Fat Buu
Babidi (uses magic and minions like dabura)
Ultimate Gohan
Gotenks
Videl (i really dont see her in but we need more females)
Kid Buu
*Movie
Beerus
So thats 22 characters with female characters, magic user, grapplers, etc for variety. If they can do 24 characters then add 17 and Dr Gero since it fits story mode. But what i really want is to start story with a Dragonball arc since that can bring even more interesting fighting techniques which ASW shines at. If its not done now then i don't see them ever doing it.
*Dragonball arc
Launch
Assassin Tao
King Piccolo
Kid Goku
My DLC prediction is basically characters they can sell but can't fit into story since that may be heavily dragonball Z based. The sequel will get remaining heroes, movie characters like bardock and broly, and the DBS tournament arc.
DLC
*Whis (magic user)
*Hit
*Goku Black
*Zamasu