Since Impossible Astronaut, I've been pretty much convinced that River is the one in the spacesuit. It was one line in particular where she was talking to Rory and said that she was a young girl when she first met the Doctor. We have seen both her first time meeting the Doctor and the Doctor's first time meeting her (or at least where told they were the first meetings) and both times River was played by Alex Kingston. I wouldn't use the words 'young girl' to describe Alex Kingston, would you? Steven Moffat has never struck me as the kind of writer who do something like that without there being a deeper meaning.
And I reckon River probably is Amy and Rory's daughter and Amy spending so much time in the TARDIS has given her a 'time head' (whatever that is

) Either that or Moffat knows that that is what people will think and has deliberately set up a red herring.
Whatever the truth about the character is, I hope that it signals the end of her time on the show. While I am a fan of Alex Kingston, I've always thought she was miscast in this role. I loved her in ER and in Marchlands, but IMHO there is something a little off about her as River. Is that just me or does anyone else see it?