Could be anybody
i think its Kabuto personally, no one else makes sense really....but i don't know if i think he was genius enough to break izanami so soon. If he though accepted his fate, then it makes perfect sense why he would heal Sacue
Yamato i believe is being controlled by the zetzu....and these were the first thoughts that entered my head, but i of course could be wrong.
i do not think its Karin, i have no reason to think Kishi would have left it the way he did if it was Hebi/Karin who approached
We all know its not Kabuto....I have a feeling its the same person that saved Madara at the VOTE