According to a GameStop flyer there is a small ad that says, "Free Limited Edition Upgrade" when you pre-order the Final Fantasy X/X-2 HD Remaster. There has been nothing announced for any kind of special edition for the Remaster, and product page for the game on GameStop's doesn't mention anything.
Final Fantasy X|X-2 HD Remaster does not have a release date as of yet but information on this date that should be sometime within Square Enix's final fiscal quarter of 2013 will be coming soon.
The game releases on PS3 and on Vita where the two games will be separate. We should be hearing something soon about the limited edition, weather it exists, and what we get for free if that is the case.