Star Trek: The Original Series was originally going to be continued via Phase II. The series was greenlit, but ultimately, it became Star Trek: The Motion Picture. Fans were hyped about the continuation of the series, and though it happened via films, the excitement remained. Now comes Star Trek: Legacy which hasn't been greenlit but is still on most every Star Trek: Picard and Star Trek: The Next Generation fan's mind.
Though fans have been pushing for Legacy since the third season of Picard came back with a flourish, there's been no official word. When Picard production designer Dave Blass spoke toWarp Factor Trek about his work on Star Trek: Picard [via Screenrant], he caused some concern by comparing Legacy to Phase II. See his quote below:
""It’s like Phase II of Star Trek: The Original Series. That actually got greenlit and was moving forward, but Legacy is just a nice idea.""Dave Blass
Although the issue with Phase II happened back in the 1970s, there's always that chance that a greenlit production can be suddenly canceled. And with Blass saying "Legacy is a nice idea," it's a reminder that it hasn't gone anywhere and could just as easily be forgotten or overlooked in spite of fan demand.
As much as fan demand has helped other Star Trek projects happen, i.e., Star Trek: Strange New Worlds and the Star Trek: Prodigy pick-up at Netflix, there's no guarantee that Legacy will actually happen even with the petitions and constant calls for the series on social media. It's simply dependent upon Paramount, and as Phase II showed, studios can change their minds even once the thumbs-up is given. So until we get a greenlight along with the casting of actors, scripts, and the actual commencement of filming, we can't be too sure if Legacy will become the next Star Trek series.