I have continued to play on PO quite frequently where Kyurem-B is unbanned so I think I have a pretty good idea of the impact it has on the metagame. There's no denying the raw power of Kyurem-B when looking at the base 170 attack stat, but in reality it's really hard to abuse it. Among other common Dragons you'd see in OU such as Salamence, Latios and now Garchomp, they're all faster than Kyurem-B, meaning it's pretty easy to revenge, and you need to send it in against something it's faster than. I think if it did have base 100 Speed it would be pushing over the boundaries between healthy for the metagame and metagame changing, but I really haven't been impressed by it all that much, like others have said before me. When laddering on PO, I really didn't find a lot of people using Kyurem, but rather using the aforementioned Dragons. The metagame right now is very very offensive, meaning teams can afford to run 5 sweepers plus a hazard setter. Teams like this generally need fast 'mons to utilize this well, which is why Kyurem is kind of a disappointment in that regard. It's all fine and good spamming CB Outrages, you might get one kill per game, but you're gonna be revenged on the following turn which heavily limits the survivability of Kyurem. I've found that Kyurem pretty much has to use Outrage to accomplish anything, meaning you're forced to stay in for another turn or two. While Kyurem obviously has much more initial power, I still struggle to find it's niche. Honestly, I wouldn't use this over Salamence or Garchomp, where the difference in speed really makes a big difference. I still wouldn't say it's bad however, I'm interested in the SubRoost set Bri posted, especially when you combine it with Thunder Wave support.
But yeah, obviously this is gonna mean a big increase of DragMag teams, as Magnezone traps all of Kyurem-B's "counters" and removes them easily, meaning you don't really have anything to switch directly into Kyurem-B. I also ran a Gothitelle + Kyurem team and that worked just as well, Kyurem really appreciates those Steels gone because literally nothing wants to switch in, the power output is scary. I'm still kind of torn on what is the best set, I've tried Mixed, Scarf and CB, but none have really impressed me. Mixed is kind of cool for removing Ferrothorn and Forretress, but you have to substitute significant atk / spA investment to beat these without letting them get up hazards / status, either making Kyurem even slower, or missing out on a few more KOs. Scarf is really underwhelming, the only choiced set it should run IMO is CB, as Kyurem can actually break through it's counters while still affording to be choice locked. Just my two cents, but after around 250 matches on PO I really didn't see a lot of Kyurem-B -- kind of hoping I can be proved wrong and someone can find a good use for it.