Although I do agree that Jericho is better as a heel than a face, his material is seriously lacking lately. I dunno if it's because his entire focus isn't in wrestling or if the heel thing has run its course. Whatever the situation may be, I think you are discounting just how great Jericho is. Just based off of what he has done, I believe WWE would make him a top face.
Face it, people are getting tired of Cena. Fans aren't as bandwagon on CM Punk as they were last year. Orton may not recover from his suspension enough so to remain on top for long. And it seems like WWE are not fully behind Sheamus as a company face quite yet. The way I see it, Jericho has nothing to lose and everything to gain from a face turn. Guess some fans just see things differently......
No, I'm not discounting how great Jericho is. Quite the opposite really.
I'm just also looking at the landscape, and seeing where Jericho is the best fit, and I don't see it on the face side of the roster.
Cena - It doesn't matter how tired the fans are of Cena (and it seems to be less recently). WWE will not turn him, and they will continue to push him as the top face. I can see the logic creatively behind a Cena turn as well as anyone, but that doesn't mean the WWE will do it. They simply get too much mileage out of face John Cena outside the ring to ever consider it (the Make a Wish thing is a good example of that).
Punk - Yeah he's been muted somewhat since last summer, but he's also been turned into the stereotypical WWE babyface at the same time. With the extended title run, and the second biggest angle in the WWE right now, the WWE seems invested in his face run at the moment. He's a better heel, and I think he's an easy turn based on his current angle (they could do a wicked double switch between Punk and Bryan right now), but they're going with Punk as a top face.
Sheamus - It seems to be an IWC meme lately to say that the WWE isn't behind Sheamus as a face. I simply don't see it. In fact, I think that they want Sheamus to eventually be the guy that replaces Cena at the top of the food chain, and that's what they're working on right now. Maybe he'll be the guy to do that, maybe he won't. It makes sense though, because Cena probably only has a few real good years left at best and the time to build the next guy is now.
Just looking at that heirarchy, it's tough for anyone to crack it. Jericho could, IMO, replace Punk if Punk is turned, but otherwise he's left picking up the scraps after the big three so to speak.
Also, consider that this run for Jericho is mainly about him giving back and putting people over. I think that in part is why his run seems a little 'off'. He's not being booked as a strong heel, because everyone is going over on him. But keeping that in mind, it makes less sense to have Jericho as a top face. He's in a better position to give the rub to the next generation of top guys by being a heel.
Could he turn face? Of course. Could he get over huge as a face? Absolutely. Could he get over enough to change the hierarchy of the face side? Very possibly... but it would be at the expense of him not being in as good a spot to put people over, and ironically, not being as benefitial to the WWE long term as he can be.