Thanks for the research on this, guys.
Frankly, I don't want to believe this means PC would be left out of New Genesis. Sega have done some remarkably stupid things with Phantasy Star particularly in the second half of the series' long life, but there has to be some limit to how far they're willing to take purposeful hostility to their own players, surely?
I mean, this is going to be a Play Anywhere title update first and foremost. It would be a lot of manual effort just to set up a new title to allow Xbox One / Series X players access to New Generation and keep PC on Old Generation. Just removing the Play Anywhere label would ban PC players from Old Generation too.
I can imagine they might limit the NG update to the Microsoft Store to start with and if other PC launchers (Steam, GOG or crappy ones) have had the game at all by 2021 they may have to wait a while. But setting up a new title? I'm not convinced. Normally Sega's player-screwing comes from negligence rather than effort.