I hope they don't stick to the tradition of introducing a whole new female protagonist, while simply revamping the male. I want to see May make a cameo with some new team members or something, but I doubt that'd happen if they create a new female..
RGBY - Red & N/A --> FRLG - RevampRed & Leaf
GSC - Jimmy & Marina(Crystal only) --> HGSS - RevampJimmy & Lyra
RSE - Brendan & May --> ORAS - RevampBrendan & ???
I'm concerned..
As for the effect this could have on the main cast? Following the tradition of the other girls, Serena would get the starter with a weakness to her own, being Treecko.. however, I would prefer that she got a Mudkip and did something with it. Oh and if she started partaking in contests, I wouldn't complain, as both hers and Fennekin's personalities could be perfect for them.. The fact she makes these pokepuff things could also go well with this..
Ash? Torchic I have no idea, perhaps he could get a Mawile or something and go on to face the all new Battle Frontier. I would like to see his old Hoenn team member as well, if I'm completely honest. Bring the reserves to the league again!