I wouldn't get my hopes up about Shadow Tag Chandelure; there's almost no way that it will be allowed in standard OU for too long. I could be wrong, but Pokemon like Genesect and Tornadus-T have already had their danger levels amplified by having a Pokemon like Dugtrio around to trap problematic checks, so I'm not seeing too much of a difference from a Pokemon with far, far more power, access to Trick, and better bulk and immunities/resistances to switch around with.
I am pretty excited for Contrary Serperior. It now has Dragon Pulse, so it can actually damage the Dragon types that it had trouble with before. However, it may not really need it. A Leaf Storm / HP Fire / Substitute / Leech Seed set would hit a lot of Pokemon really hard with the offensive coverage, and Pokemon like Heatran and Dragonite that don't fear the Grass/Fire coverage can be stalled out by SubSeed, provided Serperior is running Leftovers.
Another one I'm especially excited for is Ice Body Regice. Regice is already a good Pokemon in NU with its incredible bulk and great power alongside BoltBeam coverage, but right now it has to rely on RestTalk for any real recovery. With Ice Body, you can just spam Protect every other turn and get 25% of your health back, kinda like Poison Heal Gliscor. Regice would pretty much be like a bulkier StallRein with worse defensive typing but much better offense. It would probably be one of the best Hail abusers in RU, if not THE best.
Reckless Emboar will also be pretty cool. It won't make an enormous difference, but throwing around Flare Blitzes, Head Smashes, and Wild Charges with 20% more power is pretty cool. For an example of how this would be useful, CB Emboar currently only 2HKOs 252/252+ Alomomola 44.5% of the time with Wild Charge, but Reckless would guarantee that.