10 Reasons Why The New Doctor May Actually Be River Song
3. Old Friends
The twelfth series has been filled with the return of old friends; from the return of Captain Jack Harkness within the same episode, to Sacha Dhawan's regeneration of the Master. The Doctor is repetitively running into someone. So, who is to say that the Doctor will not run into River Song? She is a classic character who's original meeting with the Doctor we have not witnessed yet. Between her as Melody Pond and her as River Song, we do not know what happens.
This series centres around these old friend warning the Doctor. Dhawan's the Master warns the Doctor of Gallifrey, while Captain Jack Harkness is trying to get a message to the Doctor about the "lone cyberman". Both bring with them danger and confusion. This is not too much different to what River Song may bring.
Within 'A Good Man Goes to War', River warns Matt Smith's Doctor that "they are going to turn her into a weapon, just to bring you down". Perhaps, River is in hiding to save the Doctor, to prevent her weaponisation. As Gat states, people higher than herself are looking for the fugitive.