A European PEGI rating has appeared for Final Fantasy IX on PlayStation 4, with a listed release date of September 19.
While a PlayStation 4 release of the game has not been officially announced yet, there is certainly precedent for such a release. The original Final Fantasy VII was ported to the PS4 platform in late 2015, and Final Fantasy IX obtained a Steam release last year. It is likely this listing is for a port of the PC version.
Assuming the listing is correct, we'll likely get an official announcement shortly.