If a player purchases a Far Realms Setting Guide, then that is where the Setting Guide needs to discuss how Far Realms relates to psionics.
The class has to function in many different kinds of settings, mostly homebrew settings, or settings inspired by popular shows and books.
Keep the baked-in settings away from the class descriptions.
I am unsatisfied with psionics requiring Far Realms flavor:
"
Psionics indirectly originates from the Far Realm, a dimension outside the bounds of the known multiverse.
"
I refuse to purchase products that are baked-in with unwanted flavor.
The Far Realms doesnt exist in my settings. Assuming it exists is inherently disruptive, and unwanted in most settings.
The antihuman implications of Far Realms flavor contradict the personal and humanistic flavor of ones mind.
D&D 1e psionics flavor is strictly about the brain, the mind, and the nature of reality. Far Realms need not apply.
Well, guess it is a good thing that there's nothing to purchase here so far, is there?
I wouldn't worry too much about flavor-y stuff like that carrying over; most of the playtest materials often start with those kinds of details and then are removed when polished IIRC.