Shinji Hashimoto was interviewed at Taipei game show. They asked him if FFX was to be a remake or a remaster, and he said it's a remaster.
http://www.ff-reunion.net/ff/2012/02/05/sqex_news_662
http://www.ff-reunion.net/ff/2012/02/05/sqex_news_662
I'll translate what is actually said in the interview for clarification.
Q: I would like to ask Mr.Hashimoto regarding the Final Fantasy X announced for the PS Vita at last year's Tokyo Game Show. Is the game being devleoped like a HD Remaster or like a remake?
A: The game is being developed like a HD Remaster, but the visuals will be much more improved compared to the original game, please look forward to it!