While I really don't care for Eberron as a setting (the "magic as technology" trope is just too twee for me and rubs me the wrong way) I am very happy for the people who do love the setting, and look forward to the book because, even though I'm not a fan of the world, I'm assuming there still be at least a few things in the book that will be interesting new additions to use in my games.
As for the psionic Mystic class, don't forget that Eberron has an entire PC race consisting of the shards of psionic spirits cohabitating with human souls in psychically empowered human bodies. I wouldn't at all be surprised if the Mystic class was included in the Eberron setting book so you can play full-on psychic Kalashtar. My only wish for the Mystic (and my only grievance with 5E psionics, which I absolutely adore) is that they would use a different goshdang name for the class(!); Mystic is just so wrong for the name of the Psionic power-using class. Why not just use the good old name "Psionicist?" Or even better yet, why not just call the psychic class "the Psychic?" Naming a class based on psychic powers "the Psychic" is seriously kind of a no-brainer, while calling the psionic class "the Mystic" is just slightly extremely confusing. In my experience, the term "mystic" as used in modern fantasy/speculative fiction of all stripes has just about always been associated with magic.
But now that we know an Eberron setting book is coming out, I think it's a fairly safe bet that all the work on 5E psionics has been for that book rather than for a Dark Sun setting book, and to my mind that kind of explains the reason behind "the Mystic" name: it's being named for Kalasthar mysticism. I still don't like it, and would much, much prefer they just called the psychic class "the Psychic," I can at least understand why they've done it, as much as I totally disagree with it.
While I absolutely love the mechanics they've created for 5E psionics, the name of the class really irks me.