I still firmly believe that River knows Doctors beyond Eleven (like she alluded to in "The Time of Angels") and I don't think "Last Night" was *the* Singing Towers trip. No new haircut and no new suit, for example.
But now that Matt has cut his hair, maybe the 2013 Christmas Special will be the Singing Towers trip, as a totally solo Doctor/River episode. i.e. Eleven drops Clara off to spend Christmas with her dad and the Maitlands, then picks River up, they get into trouble, and at the end of the episode he takes her to the Singing Towers and she thinks he’s being a nostalgic idiot again, so it takes her by surprise when he starts crying and gives her his screwdriver.
(Again, the last time she sees him, not necessarily the last time he sees her though.)