What could it be? I'm assuming it would be after you beat both games. FFX-2 ending was not as complete as i had hoped so this 30minute bonus video sounds interesting but I dont know how it could be 30minutes long. Thats a ton of content added on to just 1 scene at the end. Or maybe it could be 30 minutes total of new cutscenes not 1 long cutscene? Either way any addition to this already fantastic story is a welcome addition in my book.
Personally, I think SE just had a lot of space left over on the disc(s). So, this just looks like "filler" to me. But, if it's really very good, then I guess it doesn't really matter.