Many slot 9 spells belong to the Psion class:
Wish = mind over matter = the essence of the Psionic power source
Foresight
Heal Mass
Invulnerability
Polymorph Mass
Polymorph True
Psychic Scream
Shapechange
Ravenous Void
Resurrect True
Time Stop
Weird
Astral Projection is appropriate for certain Psionic concepts that emphasize the thoughtscape of the Astral Plane.
In my view, any spell that is Elemental (Air Fire, Earth Water) is nonpsionic. Any spell that is a fiddly complex apparatus is nonpsionic. The psionic flavor needs to visualize or similarly focusing to "manifest" a specific outcome.
I prefer the Fire flavor stay with the Druid and Sorcerer. But I can handle a Psion "Pyromancer" subclass.
I view the Primal power source that is especially Elemental as a kind of Psionic. Psionic and Primal are two sides of the same coin. But they are distinct. Both use "soul" magic.
What about Golden Sun's elemental psynergy? This gets into the important point on the TV tropes page under Anime & Manga – East Asian media often conflates spiritual power, wizardry, martial arts, and psionics into one thing because there wasn't as much of a push back against esotericism as Europeans had with the witch hunts.
But even in the West, there's tons of examples of Pyrokinesis etc as a discipline of psionics – the important point is that the elemental magic was formed by the mind and not ritual or MSV components.
This is why I think Psionics belongs as subclass archetypes across the gamut of core classes, though there should be a Psion/Mystic core class to represent Yodas & Xaviers since they're close to the Wizard concept but Wizards are crucially far too tied to their components and spellbooks and rituals to represent this power.
Monks are the easiest next step to graft psionics onto. And as we've seen with the Purple Dragon Knight playtest, there's multiple ways to make a Psionic Fighter in 5e lore, just as Eldritch Knight, Arcane Archer, Rune Knight, and Bladesinger can all coexist (as opposed to Valor Bard/Swords Bard and Pact of Blade Warlock Hexblade Patrion Warlock really being patches that are meant to supplant or enhance the other one). I could see Psion either appearing in a Rules Expansion book a la Artificer in Tasha's, or else in a book like Fizban's or Bigby's, with a few other character options that support Psionics and a bunch of Far Realm entities for your game.
Oh and unrelateded to Yarael's post, someone said
Dark Sun has been 'cancelled' – as much as I think the setting is problematic in many ways, it's also a beloved setting and part of D&D Lore and appears by name in the 2024 DMG, so it's certainly a planned setting to explore at some point. The main D&D setting that was 'cancelled' is
Nerath because there's just not a lot of reason to include it if you're putting
Greyhawk in the DMG and besides, you've mined
Nerath for its best original stuff already (Feywild & Shadowfell, Astral Sea, Raven Queen, core Dragonborn, Tiefling, & Goliaths).
Nerath struggles to fit into modern D&D because it changed so much to support the sacred cow slaughters of 4e (their words, not mine) while also borrowing from
Greyhawk and
Mystara wholescale for iconic setting elements.
I swear, the principal reason we don't have
Dark Sun yet is because they want to get Psionics right first.