Gene Roddenberry often told actors, "I'm working on a script with you in mind..." (He told DeForest Kelley that line often in the 60s.)
Carmel bumped into Roddenberry during the early planning of TNG. I seem to recall it was at someone's Hollywood Walk of Fame Star Ceremony? I remember seeing pics of them together at such an event.
Aha, IMDb says that Carmel was a close friend of George Takei's (and worked with Leonard Nimoy on "Transformers: The Movie"). Takei's Star Ceremony was October 30, 1986. "Star Trek: The Next Generation" was announced to the public on October 10, 1986.