Oh my bad. Yeah I think it's weird how FFVIII isn't on PS4 too. No excuses.
Someone said on this forum before that Silicon Studio Thaand was shutdown? If true then it could be a problem for FFIX on other platforms. Porting ancient games like this would require some arcane knowledge on the original game code, even when it was ported with a new engine. It is best to leave it to the people who ported in the first place.