If Vince does not at least push Cena to a darker side they are completely missing out and they might as well just tell the audience he will never be heel and the a super face the rest of his life. Everyone turns heel at one time, or at the very least neutral. This horsecrap that he is a super face is not going to play well in 2012, it played well in the 80's but that is a completely different generation of fan who embraced that.
If he turned a tiny bit heel he would be so over and I think he would feel more comfortable, there is not a lot of heels left in the WWE that can take on a super face.
Either that or Brock needs to come back and play the super heel
EDIT: And RAW is proving my point. Let Rock win the belt over the next year, have Cena go neutral or self loathing then come back around while Rock gets arrogant. Cena beats Rock at a major PPV or the next WM and instant redemption and revenge.
Perfect example of why the loss was the best thing for Cena, infinitely more interesting then Cena going into the night having nobody that can beat him