...I'd say the chances of the woman being River depend on whether or not Clara's mystery is part of some nefarious GI masterplan or unrelated. If she's a weapon or a way to get to him then I doubt it's River. If her nature is not a threat to him, then it could well be River -- and Clara will also turn out to be one of the keys to solving whatever the big arc threat is this demi-season.
I have another seeming puzzle... this would seem to be how Clara got the computer-genius skills displayed in Asylum
, but if that was a future version of her why didn't she recognize the Doctor?
I suggested in the review thread that she is the Eternal Companion, existing at various levels of time.