I've brought this subject up in several other threads (and I'm sure it's been on many people's minds since Cena's recent surgery, and the time he'll need to recover). It seems the WWE is in trouble, with the amount of babyfaces they have on their roster. The only "true" main event faces they've got right now are Cena, Orton & Sheamus (maybe you could count Rey Mysterio in that group, but he's got a program with Sin Cara going on right now). The other main event guys (CM Punk, Del Rio, Big Show) are heels...the other thing is that just about all the talent the WWE has on the brink of becoming Main Eventers are also currently playing heel characters: The Miz, Ziggler, Wade Barrett, Cody Rhodes, Mark Henry, Damien Sandow (although he might be too fresh of a face on WWE TV to push as main event talent) and Tensai are the only ones I can think of in that position.
As far as faces that could eventually be pushed into the main event, the only guys I can come up with are Brodus Clay (however with his current character, I just don't see him making the leap to main event status in the immediate future), Christian (he's got the TNA red-tape holding him back right now though), Evan Bourne (not big enough height/build-wise, plus his drug stuff is holding him back), Kofi & Truth (I put them together, because it's obvious they're busy with the tag championships), Kane & Bryan (same as Kofi & Truth, although I think they're technically still heels), Ryback (it's too early to make this guy a main eventer, although he will be HUGE for the WWE in the future if he doesn't screw it up or get popped for taking "performance enhancers"), Santino & Zack Ryder (both Santino & Ryder are in that "comedy jobber" role right now, it would take a character tweak to make them main event relevant).
Unfortunately, the WWE is very low on main event faces right now (unless you were to add the part-timers; Rock, Undertaker and/or HHH). This is one of the reasons I can really see the WWE reaching out to Jeff Hardy once his TNA contract is up. I think the WWE needs Hardy more than Hardy needs the WWE right now, and Hardy could EASILY be the #2 face (if not #1 face, eventually eclipsing Cena's popularity - don't scoff, I really think this could happen) for the WWE. With the current roster, it's gotta be Sheamus as their #2 face.
A lot of people are saying Punk is #2. That may be, but he's playing a heel. I don't consider him #2, I consider him WWE's #1 heel. Before Punk went back to playing a heel (which started back at Raw 1000), Punk was the #2 face of the company...he was only slightly behind Cena in that respect, however - and at times seemed even more popular than Cena.
If the WWE is thinking about pushing a new (babyface) superstar into the main event, my suggestion at this point in time would be Santino or Ryder. You could easily put either one of these guys on a MAJOR hot-streak for a few weeks, and have them beat some big heels. I think the WWE should give whomever they decide to push a new finishing maneuver however, as I think the Cobra and the Rough-Ryder both need a change. Neither one screams "main event" finisher to me. The announcers could say that "this new attitude of (x-wrestler)" combined with "their new finishing move" are the contributing factors to their new-found success. IMHO, the WWE needs to do something right now, as their main event is gonna look pretty scarce if Orton indeed turns heel. All that would really leave as their main good guys are Sheamus & Cena. If one of them were to get injured, they'd be completely screwed (unless they start building a new ME face NOW...and I mean like next week). It's no wonder that the WWE started doing "supershows", it seems they don't have enough talent on the roster anymore for two shows. The other option the WWE has (which I don't think they'll do any time in the near-future) is to unify the belts (at least the WHC and WWE Championship) and go back to one company...I know they've kind of already done that with the Raw "supershow" and everything, but the brand extension might be in jeopardy with their current roster. My guess is that the WWE will continue to rely on Cena, however, and it looks as though they're also putting a lot of eggs in Ryback's basket (for the future). Hopefully that will work out for them, but IMHO Ryback won't be ready for the main event until sometime in 2013.
TNA has more main event level talent (at least in TNA's eyes) IMHO, and they wouldn't be in trouble if they were to lose Hardy or Aries at the moment. They could easily slide Storm into that slot, and move everyone up again. It's weird to say, but TNA has a better long-term plan going on right now than the WWE does. I know a lot of you will probably disagree with me on that, but before you blast me for that opinion - just think about it for a minute. Just my two cents.