Assume there is finally some official product for a psion/mystic class, should it then become part of the base lore and part of all settings or only for those who have extensive lore for it like Eberron or DS?
If an official book does not declare that a class or concept that underlines a class is common in a particular setting, I'd suggest it is likely still possible in that setting but uncommonly seen. Not all classes fit all settings, and WOTC should be willing to say if psionics don't fit one of the official settings. I'm not sure that they will do that, though.