I only have minor criticisms, and would probably be okay using it as is--which is a huge coming from me. So I definitely think it is moving in the right direction. A couple more iterations and it should be good to go.
I disagree with the whole "dispel magic doesn't dispel psionics." I mean, logically, it does make sense. I get that. But it also means that the Mystic has advantage to "magic" that cannot be countered, unlike every other spellcaster.
It depends on whether psionics does anything worth countering by magic. You can't
counterspell an arrow or
dispel magic a mundane disguise either. That doesn't mean that wizards have no ways to deal with arrows or disguises (or alternately, that such things have no way to deal with wizards). Dissimilar mechanics interact in pretty much every D&D session and combat round.
In the current setup, it doesn't look like psionics is really creating much that you could dispel if it were a spell, or at least, not much that seems out of line with what other non-spellcasting classes can do. Now, I only read through it once, so I could be missing some glaring issues.
As long as they make sure that psionics isn't doing the same things as magic (a design goal), and that the sorts of effects it creates can be interacted with by dissimilar mechanics just like most things in the game, I don't think we'll have a big problem with psionics and magic not directly interacting.
That having been said, I'm personally entirely neutral on the issue. Either way works for me.
Interesting to see the special rule that essentially tells the Mind Flayer "no you don't get to be special". For some reason they decided Mind Flayers aren't allowed to become even more awesome than they already are...
Right now...
I believe Mike Mearls said in a tweet that they'll probably revisit the psionic monsters once the psionic rules are out. I expect we'll see exactly the same sort of treatment as the 3.5e Expanded Psionics Handbook had. You provide a different (optional) version of the monster that replaces the spell-like abilities from the original version with standard psionics rules.
The current (well, playtesting) rule is just a placeholder for that, as well as an alternative for those who choose not to switch to "Psionic Mind Flayer" statblock when it becomes available.