I like psionics. Not in all campaigns, not for all players, but I think they clearly add something different, and after all they would still be optional. To me, what’s different about psionics is the flavor in which they are not a different kind of magic but something different, inherent to a person mental resource.
Thus, I’d like my 5E psionics to be a separate class with perhaps a couple subclasses for fighters and rogues. I would be fine with some spell recycling but the most important part of the class should be a different system, like the ones mentioned here about skill based checks.
One of the things I loved about 2E psionics was the mechanical stuff: a points pool, very different power costs, the relatively early availability of very strong powers at the cost of being able to use them sparingly, with a cost and not reliably.
I mean, in 2E if you wanted to use a power it would mean you still paid half the power cost even if you were not able to pass the power check to activate it, power check which had significant modifiers for stronger powers (more important than ever in the 5E easily achieved higher ability scores).
I also would like psionics to be able to cannibalize their own physical strength to give some extra boost to their power pool, with a cost.
This is something I like and very different from how spellcasting subclassing work (all of them). I also liked the added advantage that Magic Resistance and Psionic Resistance were not the same. I admit it brought up issues as with psionics being a way to counter magic resistant monsters, perhaps they should find a general way to figure out which kind of monsters can be psionic resistant.
As in, Golems are generally magic resistant, Aberrations are generally psionic resistant.
As to when, the sooner the better, but count me in those interested in a full fledged resource more than in an UA article.