I never liked the idea of a gray Jedi, or at least the kind of gray Jedi that’s an anti-hero who uses all the powers because he’s too cool to follow the rules. But the idea of a “gray” Jedi who does have a strong sense of right and wrong, that’s an attractive idea. The PT sets up a dogma that’s doomed to fail - anger, hate, and fear are all natural human emotions and suppressing them can be dangerous and unhealthy. You can see how this is (poorly communicated) subtext in the PT, in regards to how Anakin’s story unfolds.
I always thought that a potential sequel trilogy would confront these ideas that were floated in the prequels but never fully considered. So far, the two films (well, really TLJ) have actually picked up the thread on this to some extent - the fallibility of the Jedi, the danger/complacency of Jedi pride, the monopoly the Jedi strive to have on the Force. The pieces are in place to come to some sort of resolution for it all in TROS, if they are so inclined. Since ROTJ dropped the ball on Luke’s perspective in regards to Ben and Yoda’s actions, it became fair game to simply have Luke revive the Jedi order as it was. But now Rey is building an explicitly new order. We’ve seen Rey use what could potentially be considered anger in her fights without any condemnation or repercussions. So that could either be integrated into the storyline, or simply ignored as a quirk of choreography/acting. But on the flip, what they’re doing with Kylo’s eternally conflicted persona (never fully light or dark), and his being essentially the other side of Rey’s coin, it would ultimately be kind of surprising if they didn’t explore this idea to some extent.
When I hear “Gray Jedi” I think of someone like Cassian Andor (if he had the force). They’re doing the right thing, but aren’t afraid to flirt with evil in doing so. From that angle I can’t see Rey going towards darkness.
I don’t think Gray Jedi is the solution. You can’t say the side that destroyed planets, purged races, and slaughtered children are half the good guys now, and the people doing everything to stop them were partially in the wrong. Instead I think it’s about reevaluating the light side’s rules. Yoda says Jedi cannot have emotions, but in ROTJ, Luke proves him wrong by using Vader’s fatherly love to turn him over. Therefore, the Jedi should have positive emotions.
ANH and TESB’s morals on becoming a Jedi feel like learning anything. For example the piano. When you start you hear the piano playing a really good song, and you excitedly start learning the keys. But then when you try to play all the good songs you aren’t good, and you become frustrated. Now the teacher must stress the importance of patience and hard work.