The sources I've read concerning this have all been pretty vague; they say the scene happens after the "game's ending credits" or whatever, but
which game specifically? Because this is kind of important. If it's after X then it could be some sort of bridge between the two like Eternal Calm and if it's after X-2 then I would
like to say it's something in the fashion of maybe an epilogue to the story as a whole, seeing as how the Perfect ending of X-2 was so troutty, especially when one considers how hard it was to get 100% completion.
If it were along the lines of a prologue or exposition on the events prior, such as Braska's pilgrimage or the Machina War (I would prefer the latter, actually), that'd be awesome but I think it's pretty unlikely.
And wait, I just had a thought: it's 30 minutes of NEW content? Does that mean we'll see the FFX world in PS3 graphics?!