(Note: I don't mean to parse your post too much, I just wanted to respond directly to a few of your comments. That said, I think all of my comments below should be read as a response to all of yours, as I've tried to read yours.)
The idea would be that all of these could exist side-by-side in most worlds. That dwarf could be an Outsider. In Dark Sun, we'd have dreamers and outsiders as well (the mutation is
too mutant!). Eberron would have the Evolved as well (given the 1940's vibe, they'd make good Hollywood Nazis
). The subclasses just promote those stories into archetypes.
I mean, if your suggestions were merely for alternative flavour to with which to introduce psionics, I would have very few quibbles.
Well, for me, those subclasses and powers lack any narrative reason to exist, let alone exist independently from each other. They don't speak to what any of these creatures are in the world, how they organize, what their stories are. They're just grab-bags of powers.
The UA material made a stab at narrative by saying everything was Far Realms-y, but I think it'd be better to let psionics be diverse.
This is probably our central disagreement.
To me, if wizards deserve eight subclasses, each designed around one of D&D's traditional schools of magic, I don't see why psions deserve fewer than the six established disciplines. Aren't all the of the current 5E wizard subclasses just "grab-bags of powers" too? Illusionists are just wizards who specialize in obscuring perceptions with magic; nomads are psions who specialize in moving things through time and space with mind-powerz.
More broadly, I suppose I don't really subscribe to the idea that every element of D&D needs a specific "narrative reason to exist". Narratives are subject to the story being told, aren't they? D&D has always been about creating our own stories, whether from scratch or within any one of dozens of published settings. How can we rule concepts out of D&D for having no narrative reason to exist if we don't know the story being told? From you, "narrative reason" is just an opinion, but if WotC were to use that same excuse, I'd say it sounds like a cop-out for not wanting to translate psionics to 5E properly.
There's a tension. Some players just want some naked mechanics that they can hang any fluff they want on. 4e eventually went with this approach, more or less.
But 5e presents a strong narrative for each of the classes, and gives us mechanics to support it. The psion shouldn't be an exception to that.
I agree there's a tension, but I don't think 4E really went with that approach until the Essentials line. 4E's PH2 introduced the primal power source and drove home the narrative that primal powers came from immense spirits of creation (such as "The World Serpent"). 4E's PH3 introduced 4E psionics and tied them very, very closely to the Far Realm and the destruction of a crystal gate leading there during the Dawn War, IIRC. All of 4E had a very strong narrative that was interesting in its own right, but highly invasive and unpopular when it was applied to existing settings. (See: 4E Forgotten Realms.) It certainly alienated a number of fans when these new narratives were installed where they hadn't been needed.
I think 5E has moved
back from the level of narrative-injection that was used with 4E, albeit still not as far back as 3E/3.5E (nor as far as I would maybe prefer). When I first opened up a 1E Monster Manual, I loved the hell out of the monster descriptions because there was almost no narrative whatsoever. Monsters had ecologies and behaviours, and my imagination fired at all the possibilities. I definitely think that narrative-based design is a mistake in a broad-based game like D&D has been and is ostensibly trying to be.
