Two of the prominent minds behind Final Fantasy XII: The Zodiac Age have gone on record as saying future games within the Final Fantasy XII universe are under consideration, depending on how well The Zodiac Age is received when it releases next year.
Speaking to GameSpot at E3 2016, Hiroaki Kato, the producer on Final Fantasy XII: The Zodiac Age, said "Based on whatever kind of feedback we might get from that, that's something we'd consider [future games within the XII universe]."
Final Fantasy XII, of course, already had a sequel in Final Fantasy XII: Revenant Wings. This released on the Nintendo DS back in 2007. There is also the ever-expansive Ivalice universe too, which has seen numerous titles spawned.
We're looking forward to feedback on this new Zodiac Age version of the game. Based on whatever kind of feedback we might get from that, that's something we'd consider [future Final Fantasy XII games]. If you can put it in your article and sort of fan the flames, the feedback really makes a difference."
Hiroaki Kato, 15 Jun 2016
We also know that another Final Fantasy XII title was in development at GRIN, a Swedish developer who had previously worked on Bionic Commando Rearmed and Terminator Salvation. It was called Fortress, but was cancelled before any significant progress could be made.
In the same interview, Takashi Katano, the game's director, said they are also considering other uses for the Gambit system internally. There was talk about creating a new game based on that mechanic, but it hasn't gone further than that at this point.
Final Fantasy XII: The Zodiac Age was announced for PS4 prior to E3 2016. It will be a remaster of Final Fantasy XII: International Zodiac Job System and is due for release next year.