Director Takashi Katano and producer Hiroaki Kato from Final Fantasy XII: The Zodiac Age, were recently interviewed and asked about the possibility of other Final Fantasy remasters. Katano was asked about what other FF games he would like to remaster after his involvement with Final Fantasy X/X-2 HD Remaster and Final Fantasy XII: The Zodiac Age.
He replied with: “When it becomes a remaster, not a remake, there is a limit to how far back we can go. I do think that PS2 software was probably the limit. When it becomes a PS1 title, then we would probably have to do a remake instead of a remaster, just because the quality will not be satisfactory for the players if we do a remaster of a PS1 title. So, I fell like I’ve pretty much done everything I can do as a remaster. But, if there is an opportunity, there are a lot of other titles as well, and I will do what I can do.”
This goes back to some previous interviews with developers at Square Enix mentioning how games before the PS2 era are harder to remaster. PS1 games in particular are quite difficult which is why Final Fantasy VII is going to be remade and not remastered. Like Katano mentioned the games could be ported and slightly remastered but the difference in quality would not be very noticeable. Good examples of this are Final Fantasy IX on PC and Final Fantasy VII on PS4. Then there are NES or SNES games which can only reach a certain level of quality while retaining their 8bit or 16bit style which is probably why Final Fantasy III and IV were remade on the Nintendo DS and not just remastered enhanced ports like the PSP versions of Final Fantasy I, II and IV.