I believe that the problem with pushing Barrett is that he has been in the mid card too long. When he led the Nexus, he could have had a great, and I mean really great, title run. But then he lost over and over to Cena and then had the whole Corre nightmare before eventually getting lost in the mid card. He hasn't been a real credible threat to anyone on the main event level since the Nexus. I get that he is pretty popular and people are enjoying his gimmick, but against lesnar it wouldn't even look serious. Especially when you consider that he has a brawler ring style. Lesnar outclasses anyone in that category. Anything Barrett has to throw, Lesnar has a bigger and better version of. I don't think that most people would buy the feud, especially with Brock coming off clean wins agains Mania Taker and Cena for the Championship.
I also believe that a big reason they went with Brock is because they are trying to bring more legitimacy to the title. They gave it to Orton, the number 2 guy for much of the past 8 years or so, Cena, and Bryan only after he had surpassed the other 2 as far as being over. Now they gave it two Brock who is one of their top draws and doesn't fight for free. I think they are really trying to give more prestige to it and will continue to give it to either older veterans or top guys. I agree that this would be a major rub for someone, but I don't believe that they will give it to someone until they already reach that main even status.
The same can be said for Cesaro, for the most part. He is a physical brawler and is far outclassed in that category. He has been feuding on the mid card and hasn't exactly been dominating there.
As far as Reigns, I feel that he is losing steam. He is good, and he is over, but I think he was more over towards the begining of the year. When making my predictions for Summerslam, his match was hard to predict because I didn't really feel it mattered that much. Whether Orton or Reigns won, I feel it wouldn't have helped or hurt either. Orton hasn't really been very interesting in singles competition since Mania, in my opinion of course. I think a big part of the reason that this match/feud isn't really that important, is because it's not that personal. It is more or less just the leftover from the Shield vs Evolution feud and the focus lately has been the fact that Reigns attacked Orton before he was going to be announced number 1 contender. Rollins vs Ambrose is more personal and has been more interesting. I also like the fact that, with Rollins vs Ambrose the matches are often with other people instead of Reigns always facing Orton or Kane. Then Roman is kind of awkward on the mic at times. I will say his ring style is more dynamic and can put on decent matches with Lesnar, I just don't see him as being hot enough or good enough to take it off Lesnar.
Wyatt on the other hand, is very over, he hasn't lost as much steam as Reigns, if you ask me. He beat Bryan clean this year, as well as Jericho. I think he should have won clean to Cena at Mania to really help his push, but that ship has sailed. Wyatt has excllent mic skills and can carry the feud with Heyman. Then his in-ring style meshs well with Lesnars. Lesnar is a beast who loves to dish it out and Wyatt is a sick freak who likes to take it. I believe this is what made Taker vs Mankind so interesting in the past. On top of this Wyatt has 2 big guys to back him up.
One other name, that came to me in a dream, is RVD. I had a dream about RVD hitting a 5 star for the pin, after Heyman betrayed Lesnar(which is how I think he falls) and there were ECW chants. The problems with this one are the fact that RVD is past his prime, the double cross would be predictable, and I don't see RVD really having any must-see title feuds.