What did strike me is the whole "Run" thing - at first I was thinking, well maybe it IS River Song - just regenerated but nah. Since ever since their first meeting she's talking about running 'always running", and then Rose mentioned it. So I dunno...
Although what would be interesting is if she was a completely new race, maybe like a another Time Lord like race, but completely not Gallifraian (Sp) I could hear a line like
"Wot?! You thought you clever boys from Gallifray were the only ones who could bop through time and live seemingly forever?"