According to Square Enix (via japanese magazine Shonen Jump) the HD version of Final Fantasy X/X-2 will include a "new episode" after the ending credits. That presumably means that the sequence will play out once you've finished Final Fantasy X-2.
This "new episode" will be 30-minute long and it was written by series scenario writer Kazushige Nojima. The episode will also feature newly-recorded voices, although no further details were revealed.
Final Fantasy X/X-2 is due out this year for PlayStation 3 and PlayStation Vita. While the games will come bundled together for the console release, the handheld versions will be sold separately.