Square Enix producer Yoshinori Kitase has said the PS3 and Vita re-releases of Final Fantasy X aren't just HD re-masters of the original PS2 release, but rather a "remake". In an interview with M! Games Via Playstation Lifestyle Kitase said that the project which was revealed at TGS last September was in the early stages of development.
Kitase was a producer for the original FFX, so rest assured that the games magic will be preserved for the remake.
Kitase's upcoming project Final Fantasy XIII-2 releases at the end of this month in North America (February 3rd for Europe) on the Xbox 360 and PS3.