For those unaware, D.C. Fontanna was a television writer, who had worked with Gene Roddenberry, but is probably mostly known for her work with him on Star Trek. According to her, she was informed about the project before “The Cage” was even in production. She was a great writer, authoring some of the most famous stories of both Season 1, 2, and 3. One of them was “Joanna” or as we know it “The Way to Eden”. The latter is particularly interesting, both because it was the only story D.C. Fontanna remained uncredited on, and it represents an interesting of Leonard McCoy’s life, his daughter.
There are certainly a number of universe expanding episodes for Kirk and Spock. “Amok Time”, “Court Martial”, “Where No Man Has Gone Before” and certainly “Obsession”. McCoy’s history has always been somewhat of a blank slate, though. In 1989 we found out he had been forced to euthanize his dad, and his playful animosity with Spock is one of the show’s staples, but not much is known of his assignment to the Enterprise, or past before. “Joanna” as per Fontanna's original treatment, would have expanded upon McCoy's past greatly, revealing that he had a failed marriage and lost custody of his daughter. Joanna was to have her first, and presumably only, appearance in the series. She was to be among the space hippies that we know from the "Way to Eden", and Kirk (I know) was to have a romantic relationship with her (I KNOW!!). Having not read that draft, I can only imagine what the conversations between Kirk and McCoy were like!
However, a producer for Season 3 was for some reason very interested in giving Chekov more of his own episodes. So, the aired version has an old flame of Chekov's in place of Joanna. What's even worse, most of the dialogue between them is directly transposed from McCoy and Joanna's conversations from the original, which gives the scene of very strange overtone. However you put it, "Way to Eden" was certainly not one of Star Trek's better moments.
Now, a few years ago, I won an eBay auction for a few teleplays from Lincoln Enterprises, one of which titled "The Stars of Sargasso". Joanna appears in this one as well, and subsequently dies as well. Basically, Joanna is the last survivor of a trainee mission. The ship was destroyed by an alien named Argos, who is holding her prisoner. In a rescue attempt, a duel breaks out between the crew and Argos' androids. Not only is Joanna killed in the process, Spock is the one who accidentally kills her. It takes the McCoy/Spock animosity to whole new levels. They still don't truly make up by the end of the episode, even when Spock takes a near-fatal stab for McCoy towards the end. It's dated May 14, 1969, which is certainly a good explanation for why it never aired. As far as the live-action continuity goes, McCoy is childless.
So what's the legacy behind this? Well, the backstory of McCoy's divorce is present in the original writer's guide, and the 2009 film also referenced this backstory as well. She had a brief mention in The Animated Series, which might be canon depending on who you talk to. Additionally, Joanna herself appeared in the 1979 Marvel comics series #13. So, maybe she will be appearing in some fan episode soon. Or maybe she'll get an appearance in an IDW comic. One can only hope.