...
Personally, I love psionics so much that I homebrewed my own system for 1e based off of Julian May's books, but I wouldn't want them mandated for all settings.
Well as they are mechanics, they would need some
Sirius justification in what form they are there and why and what impact this has:
E.g. Lets just take the mindflayers and aboleths from FR being mainly hidden in the underdark, ... or the city sewers, according to some of their lore both are kind of far realm creatures, so no problem for justifying them being different and have
Sirius powers which are not conventional.
Compare DS, there the psi is a the consequence of everything mutated and it is all around, justification given again, also magic is kind of shunned and so you got another "magic" partially taking the role of wizardly magic.
But let us now assume Psionics suddenly becomes "Core" in e.g. greyhawk or FR in a way that many adventurers and NPCs are Mystics. Then that is a force suddenly, which has impact on almost everything.
It competes with wizardly magic. It competes with clerical magic (Where does it come from? Is it a gift from the gods? Is it innate good or evil? etc. etc.)
So that are two different things and it should not be just handwaved, imho .