Lots to answer, here...
If it fits into the DF why wouldn't it follow known patterns already available? Pretty sure psionics is just a classification of magic already in the DF.
Sure, that
could be a way to get psionics: Just say that it follows the mechanics of magic, as modified by the beliefs of the psionicist (as opposed to the beliefs of the magician). The DFRPG has some explicit rules you could use to model it (reaching out to other iterations of the Fate rules as-needed).
... In fact pretty much any subdivision of psionic magic can already be found elsewhere, already fitting in with its own rules and regulations ...
Oh yeah. Absolutely! As I noted, psi is often called "space magic" or part of "science fantasy."
It's those parts of "magic" that can be re-skinned with a "science" veneer; anything too inherently "supernatural" isn't really eligible to be
SCIENCE!'d ... I'd consider magic to be able to do virtually everything psi can do, plus things psi
can't do.
BUT a genuinely-psi (not a branch or form of magic) would have a different suite of limitations (see below), and a different "feel."
... The issue with trying to shoehorn nonmagical psionics in anywhere in the Dresden files is two fold. 1 it already exists as semi magical talents 2 how would it differ and what then limitations stim from that ...
Here you have come to the crux of it, or hit the nail on the head, or somesuch...
IF you posit "psi" as something genuinely different from "magic," how
would it differ? What limitations and/or abilities would it have, that magic does not?
To begin with, the standard "magic circle" would not apply. Magic (by default) doesn't block bullets, or lasers, or radio, or gaseous diffusion, or psi, or etc. -- nothing "science-y," only "magic."
Magicians
can craft specific wards and/or spell-effects that
will block any sort of "science..." but the bog-standard magic circle ward (like Harry taught Waldo, during Dead Beat) is magic-only.
So psionicists won't use those circles, except the basic sort that clued-in muggles use as basic protection.
More than once, Jim narrates how "magic" still has to "do business with the laws of physics." So Harry Fuego's some big-ass blasts of fire, when what he really wants is the ice effects from sucking that much heat from his environs; or he and Lara do the Carnal-Cannonball Express out of the Raith Deeps and into the Raith Mansion; or he and Murphy play the "Our Harley Trumps Your Buick" card. And so on.
But... these aren't all
really "doing business with the laws of physics."
Fuego-for-ice... yeah, heat-pump, got it, that's "physics..."
not. Because simply moving-around that much energy is itself an energy-intensive exercise. If that were "physics," Harry would have raised his own body-temp as a "human heat-pump" to the range of instantly-fatal, and dropped dead (or maybe dropped his temp to "semi-conscious veering into comatose").
We can accept greater level of handwavium in magic, because it's magic & need not obey the rules of physics. For "Psi," we'd need to stick closer to the
SCIENCE! of the thing; that may be a line that would need to be carefully-defined, from an in-world perspective: one might need to go into "dark energy" and "zero point energy" and "observer effect" for ones handwavium.
For now, I handwave the handwavium itself -- & all the associated issues -- in favor of asking the
story questions -- what would be the implications of this not-magic which gives "ordinary people" a magic-like ability to seemingly-defy the laws of physics in similar ways that wizards can?
Another thing (a
big thing, story-wise in the Dresdenverse) is that when "psi" is
SCIENCE!, it won't have magic's tech-hex effect. No doubt a psionicist
could do something anti-tech (it wouldn't take much telekinetic force applied directly to nanoscale circuits inside the chip-case, to render a computer or cellphone or etc as dead as any wizard's hex), but anti-tech wouldn't be the
default.
On the other hand, True-Name-based Summonings would only work as well for a psionicist as for any Muggle, which is to say some work but some do not; some beings
must come when Summoned, while others only get their sleeve tugged, and can attend or not as they choose. The "vending machine rituals" work just fine, but most others won't (needing (at least some) magical talent to cast); and still others need the power of a strong wizard bolstering the magic circle, in order for the summoned being not to promptly eat the summoner.
As you note, Harry's "Forzare" is a very "telekinesis-like" spell -- there is tremendous overlap, I think.
On the other hand, Harry's "finding" spell has no unambiguous psionic parallel. While
some versions of "psionics" include "psychometry" (object-reading) or the like, it's usually associated with the past of an item, not finding the current location of a person associated with the item; and using something like a parent's blood as a "finding" object would be "psychometrically" ridiculous (the parent's "signal" would overwhelm the child's).
So the "psi" methods -- & stories one would tell -- may sometimes closely-match those of wizards, but sometimes would be very different.