This is a genuinely hard question to answer because it's just not the structure of 5E books, like not even one.
I expect if they did this, it would mark a significant change in direction.
As such I would expect a much more in-depth Psion class and probably at least one other class that isn't the Psion but shares abilities with them. Normally I'd think that'd be the Psychic Warrior but that already exists, so maybe they'd go with Ardent, maybe also the Battlemind even but that would be pretty wild.
I'd expect to see any archetypes that WotC considers "Psionic" to be reprinted, and because this is a 5E, probably psionic archetypes for several but not all classes that don't already have them.
Psionic wild talents would likely get recast as "Psionic gifts", and there'd be some Psionic-specific Feats as well.
Probably see a whole bunch of psionic monsters, including some previously oriented towards Dark Sun only/primarily. Advice on changing over existing monsters to Psionics from magic,
Likely extensive advice on running a "psionic" campaign, including like, never calling Psionics psionics, and just treating it as the "default" magic of that world, because it actually is a lot closer to the magic of a lot of fantasy media than D&D magic is.
I think we'd see the CRYSTALS CRYSTALS CRYSTALS ALSO WE LOVE THE X-MEN!!!!! vibe of 3E severely curtailed. It's a dumb and tacky approach to psionics that also limits them hard theme-wise. So mysticism/spirituality would likely be the main thing there, and as they aren't casting spells, they don't need focuses. Someone will of course get terribly upset about the lack of VSM components, but this can easily be worked around by making some abilities flashy/obvious, and others just more limited or costly because of their ability to evade that kind of detection. It's not a huge issue anyway in my experience - I've played countless RPGs where a lot of magic and/or psionics and/or The Force or the like had no VFX/VSM stuff and it wasn't really that much of an edge.