I know it wouldn’t ever happen but I’d prefer if they actually followed through with their original intention in SF3 to not bring anyone back and leave out Ryu and Ken. Just to make us learn to like some new characters (look at how poorly adopted almost every new SF character was in SF4. Gouken, Juri, Hakan, Abel, Rufus, Viper, El Fuerte, Seth, Oni are all new characters.
Rufus, El Fuerte, Hakan and Seth are among the least popular in terms of the fan base (Rufus is played a lot but that his moveset is good not because they like the character.)
Juri and Viper are pretty popular in terms of their fanbase but neither are played terribly often (Viper is decently popular but even though Juri is by far the most popular new character hardly anyone plays her.)
Gouken, Abel, and Oni are pretty much middle of the road nobody cares about them. There aren’t that many people who like the characters for their move set and there aren’t that many people who like their designs.
Don’t get me wrong, I’m not complaining about any of those characters designs or their move set (I kind of like all of them except Seth and Oni both of whom are still fun to play as but I vehemently dislike their design.) I’m a big fan of Juri and Gouken but they simply aren’t played by many people.
I’d love a SF game with no Ryu/Ken/Akuma/Chun for ONCE.
Hell, if they continue with the SF3 story arc I think Yun and Yang could make for a good pair to be the “main characters” of the series. If they continue with Alpha I think they should strongly consider Cody and Guy who have important roles in the Alpha storyline (mostly Guy) and a large fanbase.
An SF game with no returning characters would be cool and allow designers to flex their muscles and create some really interesting new characters or new takes on old ideas. (A shoto clone with new properties / way of using their moves would be fine in a game where Ryu and Ken aren’t already in it.)
None of that will ever happen though.