UPDATE 2: Confirmed via CapKobun, X8 is a PS2 Classic on PlayStation 3. Nevertheless your input is still being gathered on the prospects of a PS4 version.
UPDATE: While the game is currently slated to hit PSN today, it has come to my attention Sony did not specify which console - PlayStation 3 or PlayStation 4. The game does not have a hub on PSN yet; merely referenced here in a holiday lottery as an eligible prize. We'll keep an ear to the ground.
Original post: Mega Man X8 is set to arrive as a PS2 Classic on PlayStation 4 today in Japan.
No word yet on availability outside of Japan... stay tuned!
Source: PlayStation Japan