From where I was sitting Cain had no chance at Taylor whatsoever. He was playing back in no doubles defense and Taylor saw the play in front of him the whole way. And you also don't know if Cain's ankle affected his ability to plant and throw.
They spent about 5 minutes going back and forth on that play in the TBS post-game. Rollins says he would have been out there, yelling at Cain not to throw, Sheffield saying he would have ignored Rollins and thrown. Replays looked like there was a possible play if Cain throws right away. You might be right about the ankle and not planting, and maybe the SS blocks his view of 3d, but, fundamentally, it was a risky play by Taylor given the game situation.
Edit - I agree that Rollins and you guys are right. Even if a play could have been made, it is Zimmerman's run that matters. Cain can't throw unless he knows he nails Taylor.