The preliminary calendar for the 2015 season is out! Link
The idea of World Tour finals will be finally applied in 2015 after FIVB decided to withdraw it this year. New Major Series will be introduced. To be honest, I don't get their importance or role. There are the usual Grand Slams and Opens, the prize money for the Majors seems to be the same as of a Grand Slam. Perhaps they will matter more for the Rankings, who knows, it's not well explained.
Lucerne, Porec, St. Petersbourg (in USA, not Russia), Yokohama and Sochi with planned WT debuts. However, FIVB are known for changing their program often, so let's wait and see.