Parmandur
Book-Friend
(sorry, I keep hitting the "laugh with" button because of my fat thumb). The Mindflayer/Gith conflict was played up in Volo's Guide. If there is a second Volo's style book, with the Gith in it, I would wager we would get more on that line.True. But Spelljammer is a very different animal from the Planes.
There's so many awesome extraplanar monsters, forcing Mind Flayers into such an adventure feels like a waste.
There's probably a great Gith/ Mind Flayer story planned. Or the potential for one. I don't think the three have ever had a big story focused on their conflict.
But that doesn't feel like “the planar adventure”. That feels like a story set on the Realms with the world under threat from both the Githyanki and the Ilithids.