The recently released issue of Dragon Magazine has announced the official title of upcoming 4th series of the TV series Slayers. Slayers Revolution which is, to my knowledge, still without a release date was announced in the March 19th issue. It was not confirmed, but hinted at that the character Xellos will be the main character and not the popular female lead Lina. It was also reported that a major announcement will be made in the next issue of Dragon Magazine (going on sale May 20th, it is released bi-monthly.)
Dragon Magazine published the original light novels that started the franchise.