In terms of changes they could make to the metagame, there are a variety of possibilities to consider. The first and foremost would obviously be new Pokemon, of which (to our knowledge) there are only two of: Black Kyurem ad White Kyurem. Whilst their stats and abilities have not yet been released, it seems Black Kyurem is very powerful physically, as would be assumed of a Pokemon that seems to derive from ekrom. In the Reshiram VS Black Kyurem battle on Pokemon Smash, a single Freee Shock was enough to OHKO a Reshiram of the same level. While it does receive STAB and Reshiram;s Physical stats are obviously tower than its special, this may suggest that Black Kyurem's stats may be HIGHER than ekrom's. In terms of the aforementioned unknown ability, when Kyurem attaches it's tail to it's wings via the "wires" of energy seen in their sprites, Ash refers to it as "Overdrive", which may provide evidence of a new ability as well. That aside, Keldeo and Meloetta, due to their revelations and distributions, will also be legal on Wi-Fi as of now. The most probably and influential change with BW2 to the metagame would be in terms of move distributions, in my opinion, Just like with Platinum, the developers and programmers have the opportunity to give Pokemon moves they did not previously have access to, either by tweaking their level-up moves, or introducing more Move Tutors. It is very possible that a mere move or two may alter a Pokemon's tier due to their usability. For instance, if Regirock were to obtain Head Smash, and a reliable recovery move, it may become more prevalent. Relicanth obtaining the same move (along with its ability Rock Head) moved it up in both tier and prevalence due to the synergy of the two, and as a result this obviously presents a possibility.

That aside, what are your thoughts on how the Metagame will change?

The two Kyurem forms are interesting, but also hard to predict. Originally, I though their types would be Ice/Fire and Ice/Electric, but instead, they remained as Ice/Dragon. Now this type offers few resistances, while its weaknesses remained as Dragon, Fight, Rock and Steel. All of those are extremely common in the OU tier, unless you want to exclude Rock. Nevertheless, the fact that these two are in danger of Bullet Punch and Mach Punch remains devastating. The Uber tier is also filled with fast Dragons, so unless these two forms don't have the speed of Kyurem, they might suffer as well. The presence of Stealth Rock doesn't help them as well.

To make it clear, their stats should be as high as Zekrom and Reshiram or probably higher. This, on its own, can out both forms in the Uber tier. Nevertheless, I doubt they would succeed as much with many bulky Steels roaming around, armed with Stone Edge, and sometimes Bullet Punch.

If their stats really as high as I think, that alone will send them to the Ubers tier. I mean, Garchomp got in because it had moderately high attack and moderately high speed. If Black Kyurem can OHKO Reshiram of the same level, that suggests maybe Black and White Kyurem will have ridiculously high attack and special attack (respectively), but possibly fall short in something else (most likely speed).

But judging by how Smogon rates the tiers, if they don't put the Kyurems in Uber immediately, they'll put them both there within a week or two.

I say throw the Kyurem's in Uber, just not the Regular Kyurem. They seem to be overpowered and would make a great addition to the Uber Tier.

But Keldeo and Meloetta..

Well Keldeo is great offensively in both ends and seems to have a respectable defensive stats too. Really what Keldeo is a Water typed special attack stat'd Terrakion! Though you can set a Calm Mind set, its possible to make a Swords Dance set. Though I think it would be outclassed by Terrakion, it works the same way and even has justified. Calm mind is the better option though as with 2x Sp. A, it matches the 4x Atk that Swords Dance would give if given the right EVs. So I think it would make a good edition to... UU?

Meloetta has an odd typing of Normal Fighting or Normal Psychic. Eh im too tired to write... I think its gonna be in OU. Its stats are amazing! Besides for the Physical stats its amazing. I think the Pirouette form will be the more popular one. It has more of a sweeping potential.

Wait does anyone think that Genescect is gonna be released?