From what it looks like, they aren't planning on putting Dragonball or Dragonball GT characters.
With that said, Garlic JR., DR. Wheelo. Lord Slug, Great Ape Forms (like Tenkaicihi 3, but then they would have to have all the "LARGE" characters like Full Powered Lord Slug and DR. Wheelo) Kind Cold, King Vegeta, Hurcule, and Uub (as far as the top of my memory).
seeing as though they've used most of the main characters for rb1 then went to film specials for rb2 i cant see where they would go, maybe a new ss3 only vegeta deserves it but according to kids every one needs to be able to transform, on this topic only bardock seems to be the only saiyan i would like to see transform
They should really focus more on each character's uniqueness. For example, take a look at Tarble's moveset. He doesn't have anything exclusive, except for his Ultimate. I know he doesn't do much in the movie but they should give these characters something unique. And treat transformations like an actual power-up, rather than a different character. ,
Why worry about tomorrow. It will be gone the day after. "If I fight seriously, the whole Earth could be destroyed." - Vegeta
It's a lot harder to get to Kaiokenx3 then it is to hold down RT and transform into SSJ3, so it should be stronger. If you let your opponent get Kaiokenx3 you deserve to get the beating of a life-time.
http://s1.zetaboards.com/Shenrons_Wake/index/ - A place to discuss Raging Blast, without all the drama.