Final Fantasy X/X-2 HD Remaster launched today in Japan, along with the game's ultimania. In the book, there's an interview with Final Fantasy X's scenario writer Kazushige Nojima, and he states that Final Fantasy X-3 is a possibility if there's demand.
"If there's enough demand, then we may possibly see new developments. I would personally like to see a sequel like X-3," said Nojima when asked about a possible sequel. With the release of the Final Fantasy X-2.5 novel, which happened today as well, it seems likely that Square Enix is aiming at a Final Fantasy X-2 sequel.
Final Fantasy X/X-2 HD Remaster will be available in North America on the 18th of March, arriving 3 days later, on the 21st of March, in Europe.