I still think WWE ought to take a shot and turn him full heel again. SuperCena has gotten stagnant.
When his merchandise sales dry up, then they'll turn him. Trust me, it won't be THAT long a time to wait, considering we're in the midst of generational changes in pop culture right at the moment.
If by some small miracle, WWE manages to push Sin Cara to the main event, and at the same time manages to market his character to an International audience, then I could see the former Mistico overtaking Cena in terms of merchandise sales.