As of now, I could not find any source on the internet yet, but I’ve heard from Imagine-Nation (NHK) that Prince of Tennis will get its sequel soon. I believe the manga is already ongoing but the anime won’t be here earlier than the first month of next year. The manga will still be published in Weekly Shounen Jump, 週刊少年ジャンプ!
As an overview, the whole team will face all other schools from across Japan – one that will include some sort of qualifiers in which Ryoma will eventually lose. Yes, that is a cold-hearted spoiler, the way it has been said in the show. I might as well share it to you. 😛