I'm curious as to why the wu jen is being stuffed into the psionic class—it's pretty out of nowhere and no basis in the game's history. In fact, "wu jen" literally means "magic person" and was a term coined for the 1e OA, and loosely inspired by Taoist wizards in Chinese folklore. Magic. Not psionics.
....
Still, if there’s serious intent to bring the wu jen to 5e, just make it a wizard archetype, and convert some (read: all) of the old wu jen spells.
This caught me by surprise, as well, and my gut reaction is similar to yours.
I realized, though, that I have no idea of the origin of the term "wu jen" and whether it even existed prior to the 1E OA. If psionics is now ki, and ki is the Eastern mystical life energy, then I can see where using the term for a sort of psion/Mystic focused on more "flashy" powers makes some sense.
Now, that said, I'm still amazed by just how varied they managed to make the Mystic sub-classes. That one class has what, in former editions, were a handful of very different classes: a warrior, an assassin(ish), and a couple different kinds of specialist mages. It's very impressive that the 5E class system is that flexible, but I find myself wondering if the Mystic isn't a bit too broad. It's almost like a gestalt class that's separated by power source instead of role (combat, skill monkey, caster). I'm not sure whether that's a good thing or not, but it does make me wonder if 6E* could be made to look a bit different, with Rogue, Ranger, and Barbarian rolled into sub-classes of Fighter (or Warrior or whatever) that has its own, robust mechanic that all the classes could draw from to blend skills, combat maneuvers, etc. Likewise, Paladin and (maybe, but probably not) Druid could go under Cleric (or Channeller, etc.) with a similarly coherent mechanic to interact with divine powers that is different from the way arcanists do. It's an interesting idea, but I don't think I'd want to see it play out beyond the pages of a UA/DMs Guild article.
* I'm not speaking about a literal 6E. Instead I'm just giving a name to a hypothetical gestalt-by-power-source structure. I'm also not advocating for it, just leaving some brain droppings.