Square Enix has been making solid remasters of their PS1 Final Fantasy titles for the past year or so, with FFVII-IX landing on PC and VII landing on PS4. But either in the future or planed in the past, the PS Vita platform was under consideration for a version of one of these remasters.
Final Fantasy IX Remastered came out last fall on PC and Mobile, but coding inside the game for the PC port in addition to the below image suggests that a PS Vita version was planed at some point or still is coming.
Personally, I doubt the game is still landing on the Vita as the original can be played as a PS One Classic on Vita. But with the success of FFVII Remastered on PS4, I wouldn’t be surprised to see the port land on PS4 in the future or even a cross-buy/cross-play version of FFIX releasing on PS4 & Vita some time this year.