I REALLY hope my Fanatec setup works on the next Xbox and PS3. I will be seriously pissed off it doesn't with how much money I threw at that.
99% it will.
NextBox will continue to use Xinput (XID) while PS4 will 100% continue with HID and USB support.
Some firmware for Xinput 1.4/1.6. will be probably be released with time, but IMO it should work with no probs.