Eh, I figure I'll post my thoughts thus far~
My general impression is that RU this gen has an insane amount of set up sweepers, you'll honestly find at least one per team. This meta is all about bulky offense and assisting Pokemon X in sweeping. It's overall really fun. I mean you can run just about everything from Froslass hyper offense, Escavalier balanced, and Cresselia stall. I really like RU this gen there's just so much to use and a shit ton of variety. Oh, and one thing: Knock Off spam. Be prepared. ;)
So far, this is pretty much the top 5 threats in XY RU (not sure about order, but top 3 could be rotated in any way):
1) Zygarde
2) Suicune
3) Kyurem
4) Escavalier
5) Reuniclus
If you're not specifically preparing for these guys when team building, you're doing it wrong.
I'm not sure about a top ten, considering I haven't played as much as I would like to make a clear estimate, but Cresselia, Shaymin, Entei, Milotic, Pangoro, Gothitelle, Tornadus, Scrafty, Froslass, Flygon, and/or Yanmega would probably be the closest to that range. They're all notable threats in this meta as well.
I know it's premature, given that this isn't even official yet, but lemme talk about
the broken shit possible suspects.
Suicune: I really dislike this Pokemon. I think imanalt pretty much hit the nail on the head with this one: Suicune has no checks, only counters. This I agree with because unless you carry something specific to beat it, it will over power your "checks" and sweep. That's not to mention those suicune vs suicune pp stall wars are just a bunch of drawn-out snooze fests. It's not fun to use nor play against. This Pokemon brings really nothing positive towards this meta, and all it does it just stifle the flow of the match with its absurd bulk and Calm Mind. This thing is probably going to end up as one of the first suspects if not outright quick banned.
I prefer the former.
Zygarde: Yet another Pokemon on my personal hit list. Similar to Suicune, this thing has no checks, just counters. My main beef with Zygarde is its ridiculous bulk, which lets set up on 90% of the tier with minimal difficulty. That's not to mention its range of sets in Coil, Dragon Dance, and Even Choice Band to through you for a loop. It's difficult to even check b/c you have to figure out the set, but by the time you do, it's usually too late. =/ Versatile + Phenomenal Bulk + Great Coverage + Amazing set up moves... yeah. You get the idea with Zygarde. It and Suicune should share the same fate.
Kyurem: Out of the current three titans dominating RU atm, this is honestly the least worst of them all... My reason for that is b/c you can actually check this thing, lol. The currents viable sets I've used / played against are LO, Specs, and SubRoost. Now, the issue with Kyurem is that pretty much every set it can use causes problems. Unlike the that last two, this thing can be checked, but not countered... I mean it sits in a weird position where most teams can check it by default, but at that same time, it's impossible to counter b/c it can run any subset of moves to bypass pretty much everything in RU. You're going to lose something each match when playing against, it's inevitable, but at least your team won't be outright swept. I think this will lead it to being suspected / quick-banned within the future, but it isn't on the same level of ridiculousness as Zygarde and Suicune...
More on stuff later imo