That’s the possibility raised by Kingston on BBC Breakfast where she hinted that her time travelling in the TARDIS may not be restricted to just the tenth and the eleventh Doctors:
“[River] met a Doctor in the future – which is my past – and that Doctor is a person [she] had a very strong relationship with. But it may not necessarily be this Doctor.”
Of course the only person who can answer that is Chieftain Moffat who’s not exactly willing to spill even the slightest detail.
Regardless of how many other Doctors River will flirt with Kingston also told Doctor Who Magazine that as long as her character continues to grow she’ll keep playing her:
“It’s not often, as a woman, that you find such a fabulous, kick-ass role to play, but I think, in order to make her a fully-rounded character, there have to be real, hidden emotional depths that are slowly revealed, so I’m loving all that. She’s an amazing character.
“I love playing her, and I love that she’s been embraced – not just by parents, but also by kids, because that makes her sort of ageless. She’s naughty, irreverent and fun…and she gets the best entrances and exits every episode. Nothing is too bizarre for River. She’s fabulous.”