To be honest, I see him becomin stales much quicker than that. Usually a character is fresh for 3 years once you have hit your prime. Orton hit his prime in '09.
The fans are ready to move on after that.
The cheers are about to beome "polite" cheers. And in 6 months the booing will start.
Now that is all predicated on the thought that everything remains the same.
Right now is the perfect time for a huge heel turn. And it should be done at WM.
After WM, he should move back to Raw to do a 6 month program with Punk, teaming with Jhonny Ace. It could be done in the manner of the Cena-Punk fued.
But if WWE has a Cena heel run planned anytime soon, none of the above will happen.
If Cena is to remain face, he should be moved to SD After WM.