I think whoever/whatever she turns out to be will never quite live up to the speculation.
I personally don't feel that she needs a secret identity to be awesome. She's River Song and already a badass. Her character makes her cool, not the possibility that she may be The Master or the Doctor...imo.
that said I do think it was made quite clear with DT that they had a romantic relationship, possibly marriage-though that in itself is unlikely to be something we will ever see, since our Doc has a companion and i can't see him getting hitched yet...although he already knows how she dies so maybe...

okay thats utterly doubtful-unless them getting wed is a plot device rather than another love thang?
I think my brain would melt if she turned out to be some weird fangled Master/Doctor/Pond concoction!!