I may be wrong (I usually am), but I have a feeling that if there are going to be any new pr/evos for old pokemon in future games, they won't be for any Gen I to Gen IV pokemon. I say this because Gen V gave us a fresh start - it's nowhere near the other 4 regions, the route numbers have been reset and all the pokemon we thought could be related to old pokemon (especially Alomomola looking like a Luvdisc evo) turned out to have their own separate evolution lines/families.
And look at the similarities in the names of Zubat and Woobat. One may think that they were related in some way from their names alone, yet they'd be wrong.
In short, what I'm trying to say is that some Gen V pokemon look like they have their own counterparts from previous generations, so I don't see why Gamefreak would go back to giving pokemon from the first 4 generations more evos or prevos. If anything, they'd do that to Gen V pokemon.