Honestly guys, I really don't see this going anywhere that it hasn't gone before. For one, Nexus will still mostly be about trying to get one up on John Cena, which is where I think the writing made the big mistake of going in that direction in the first place.
Punk is already just as obsessed with Cena as Barrett was, hell he probably will be even more.
Second of all, why bring in a new leader in the first place? It would've made more sense just to put David Otunga as leader, since that's where they were going with it anyways. Why try to oust another leader in a struggle for power when you are just gonna bring someone else who is very similar anyways? Like replacing Stalin with Hitler.
Third of all, CM Punk hasn't been booked to look like anything special since the beginning days of Straight Edge Society. At this point, Punk has pretty much taken the place of Jericho as being the veteran guy who the fans still care about who is only used to put younger guys over and serve as a filler when the main event pool looks to be drowning.
I don't see this going anywhere special. At least we thought Barrett actually had a chance against Cena. CM Punk has none.