I agree. I would much rather have Jason or Shannen return. It would make more sense for Jason to come back so that Brandon and Kelly can be reunited. I don't know what they would do with Brenda if Shannen returned without Luke. For some reason, Tori seems more interested in returning than anyone else.
Well Tori obviously wants in, since 90210 started her career. And her father always visioned a new generation of 90210.
But I agree, Jason's return makes much more sense. Brenda left after S4 and hasn't made a single apperance since, so it seems off. But fans love Shannen, so if Shannen is in the series will become a hit.
Honestly the characters I want back are. Brandon, Steve, and Valerie(although Tiffani stated she is out).