"As much as many playtesters enjoyed the psionic themes in the mystic, feedback was also clear that the class encroached on other classes’ territory and that it was often too complex, too powerful, or both. Following that feedback, we’ve decided to say farewell to the mystic and explore other ways of giving players psi-themed powers, as we did with the features of the Great Old One warlock in the Player’s Handbook. In 2019 and now in 2020, we’re enjoying that exploration, looking into providing options (subclasses, spells, and feats) that allow different types of characters to manifest psionic power. The philosophy of this approach is most akin to the one taken in the 1st edition of D&D, where psionic powers weren’t the domain of any particular class but were available for characters of different types to experience.:
Read the writing on the wall man. They've abandoned a dedicated Psi class (which is what most people seem to mean by "Psion"). I don't think it's coming back. At least, not any time this year.
Sounds more like they are abandoning the idea of the "psion wizard" wizard. The mystic that is a reskinned wizard.
AKA the complex OP psion(icist) of 2e and 3e.
Note "the encoached on other classes." The class with "psionic knock, psionic fly, psionic grease, psioinc indentify,and psionic magic missiles" is dead in 5e.
I can see the return of the more limited 4e psion. One focused on the core 6 psionic schools only.