I have River and Rose meeting in one of my fics as well -- River runs into Rose right before the events of "Army of Ghosts/Doomsday" and there's so much she wants to tell her, but can't. A second half-formed idea has Ten II turning into the Valeyard and is the one behind the Silence and Rose seeks help from her original world and gets it from River, and they're the ones who wind up saving everyone from the Silence.

I think your headcanon is just beautiful. Maybe River was the one who really brought Rose the bike -- or made the Doctor think he came up with the idea. ^_~