Keldeo is a huge threat, will definly be in the top 10 usuage. The calm mind varient is really hard to stop as it can hit on the physical side thanks to secret sword and if you run Hidden Power (ghost) you have perfect coverage. Also the specs varient is extremely poweful in rain and base 108 speed means thats its pretty hard to outpace without priority. Id expect that when Keldeo is released that rain teams will find more usuage again.