New Day SEEMS to be gaining some ground as they're in the process of a slow heel turn. It's still too early to tell, in my opinion, but I like that WWE is making fans wait for the Lucha Dragons to get their first title opportunity. I think we might see a bit more of a transition in terms of look and overall attitude from New Day as time goes on.
As for Fandango, he's gone as far as he's going with the gimmick. A gimmick like that has a short shelf life and can only take a guy so far. He's worked hard with it and has gotten over to a decent degree, but he's not someone that fans are going to take seriously as a threat to a singles championship and putting a singles title on him will only be met with derision and criticism from most fans.
In terms of The Bella Twins, Nikki has always struck me as one that's more of a natural heel. How she's portrayed on Total Divas, though I'm sure some of it is exaggerated, is she comes across as much more shallow and materialistic than Brie. Brie comes off as someone that's generally more down to earth, doesn't spend money as if it's about to go out of style and prefers a generally "simpler" sort of lifestyle. As far as Naomi, she's got potential as a heel. She's got personality and she's entertaining in the ring, at least most of the time, though she needs to ditch her current entrance theme and should adopt a new finisher. The Rear View is one of those goofy finishers that just doesn't really make much sense and it just doesn't strike me as a heels finisher.
As far as Kane goes, he's someone that's never gotten as much credit from fans as he deserves. Since the late 90s, Kane's been a very strong and reliable presence in WWE's upper mid-card picture. He's been very good in his role over the course of the past few weeks and when he injects that angry passion into his promos, he's highly entertaining. I could see Kane leaving The Authority before too long due mostly to Rollins' constant needling of the guy. I don't see him costing Rollins the title, another Randy Orton title run just doesn't hold a ton of interest for a whole lot of people, but he might come close.
As far as Bo Dallas goes, much like Fandango, Dallas' gimmick is one that's only going to take him so far. While his character can be pretty entertaining sometimes, fans aren't gonna take him seriously as a credible threat to a champion. Given a more serious sort of character, I think fans could get behind him as he has a good deal of personality. As far as his in-ring stuff goes, to be honest, we haven't really seen a whole helluva lot out of him, but he doesn't strike me as anything special. However, Dallas as IC or US champ right now will only undo whatever progress has been made with them over the course of the past month or so because, as I said, he's just not someone who comes across as a serious threat to anyone and the Intercontinental Championship especially has had more than enough lame duck title runs over the past few years.