Jericho would have to get out of his contract first. People were treated worse then Jericho. RVD was a bigger misuse from WWE and you don't really see him slamming WWE left and right. (Hell, he did it more during his tenure then he has since leaving). Like any mainstream place would give a fuck if a wrestler wasn't put in the main event.
Shawn-Punk would be a mess. Not only that, I wouldn't want to see the negativity leading up to it. Shawn-JBL really sounds good to me now that I think about it. The promos should be fantastic. The best choices for Punk would be the aforementioned JBL idea, Finlay/Umaga or maybe Mysterio.