The official Pocket Monsters Best Wishes website has announced that a new ending will air on the April 7th, 2011 episode BW29 - The Horror Stories of Hitomoshi Mansion! (ヒトモシ屋敷のこわ~い話!). The ending is called "Can You Say the Pokémon? BW" (ポケモン言えるかな?BW). The song has a very fast tempo like the previous naming songs. A couple screenshots from the ending were posted on the official site and can be seen below.
Nice ! And here I was wondering when they were going to have a new ending. Too bad there's no way to get a preview of the said song... well, guess I'll just have to wait a few more days.