It's already been on PS4 in Japan for a little while. (In Japan, I believe PS4 & PC/Xbox One versions of New Genesis launched all on the same day?) (And then before that, a PS4 version of regular PSO2 came out in Japan in 2016 and there was even a Vita version before that.) (Similarly, PSO2 and PSO2 NG are available on Switch in Japan too, but only through Cloud Edition streaming.) Internationally, this was an Xbox exclusive (along with PC) until now, but in Japan it has been multiplatform here and there for most of its existence.
So this is probably just the end of timed-exclusivity or whatever marketing approach SEGA had to focus on Xbox in the Western markets; it's not a "new platform" version being launched. But it's good for everybody who didn't get to play the Xbox or PC versions that now there's even more PSO2 to go around.