Yes, the submission-without-agent part was what made TNG's spec script policy so exceptionally liberal.
As I recall from Gerrold's book, (1) he needed an agent (any agent, regardless of whether he or she was any good, so long as he or she was WGA-recognized) to submit anything, (2) he was expected to join WGA as soon as he'd made a successful sale, and (3) once he was a member, he was forbidden by the WGA to work on-spec.
Of course, that was how it was over half a century ago, and it's probably been close to half a century since I last read either of Gerrold's books from that era, so I could certainly be mis-remembering a good deal of that. (Although I certainly recognized his "Tomorrow Was Yesterday"/"Yesterday's Children" story as soon as I was a few chapters into The Galactic Whirlpool!)
If somebody were to circulate a petition to CBS/Paramount, S&S/Pocket, and Diane Duane, begging for a new ST opus by DD, I would be the first to sign it. And yes, I'd sign a similar petition for a new ST opus by GC (which would be one less petition, since he expressed willingness in the idea, in this very thread). But I have my doubts that such petitions would have any effect on the "suits"; they're almost as bad as the late Steve Jobs was, about being convinced they know what the public wants better than the public does.