Okay let's take your poll choices one by one.
Dolph Ziggler missed his chance at regaining main event statue after they did nothing with him last year at Survivor Series. He came out as the sole survivor and I really thought okay they would push him again. Instead he ended up in a lame story line which not only took him down a few pegs, but Rusev and Lana as well. I won't count Summer Rae as she was already a few pegs below them anyway.
Rusev again after the horrendous story line between him and Ziggler it might take awhile to get him back to where he was before. Not only that, he is just coming back from injury, and that's the second time this year he's been out. I'm hoping he doesn't get the label "injury prone" and that stalls any push he might get. It also seems that McMahon was furious with both he and Lana for getting engaged and breaking kayafe. He'll hover around the top of the card, but a sustained push I just don't know.
Barrett I love. He is great on the mic and in the ring, and I have no idea why he's been held back. He should have been pushed a long time ago. I guess though injuries have taken their toll and maybe he's being seen as a guy who had two pushes and two injuries resulting from them. They might be wary of giving him another one. Again he's the type of wrestler they can move around anywhere in the mid card.
Stardust is just too out there, and creeps me the hell out. The gimmick while played brilliantly is just too comic book for my tastes. Plus they've stuck him with the Ascension which is never a good thing. That team has been totally ruined by Vince's manipulation of their gimmick. I think the boat has sailed a long time ago for Rhodes and he will be mid card for the rest of his career.
Neville, I like. His biggest issue is his size. He's just a bit on the smallish side. He can go like a mofo, and he's a true high flyer, but I have problems believing he can beat much bigger guys. No I don't mean slowpokes like Big Show and Mark Henry. I mean someone like an Alberto Del Rio, is is tall, fast and very technical. If Neville had another 6-8 inches on him, he's be up near the main event picture no problem.
So like someone else said, you just can't take any of these guys and throw them into the main event scene and make them believable to win the title. If they do go into a title match, then it's for sure they are coming out the loser. A build takes awhile, and with Cena due back in a few weeks, and the push still on Reigns, the WWE doesn't seem to have the resources to even bother with the mid card for now. The time to elevate them was when they had a full roster, and they could have changed up the matches every week or so.