I... agree with you about Neogi and Intellect Devourers. That's the sort of direction that I was headed. They both have a bit of baggage though and, of course, no rules, per se.
If I could put it in a sentence: Illithids are the "big evil" and are served by patsies; so lower level threats (thinking like levels 3-5) would involve, generally speaking, fighting "good people turned bad by mind control".
It's fantastic, from a tragic drama standpoint. But DnD players will, generally speaking, prefer to fight evil guys at least for "final fights". Obviously you can punt a bit, and have evil-mind-controlled-wizards-who-were-evil-before or corrupted-githyanki; or "astrally projecting illithids who are much weaker" or something like that.
Or we could work to create something like the blues, (the psionic goblins from 3.x). Improved version of an existing evil race (somewhat like ogre -> ogre magi).
There's a lot of goblinoid material but goblins are solidly "entry level".
They could be psionic enough to be powerful, but not so psionically gifted to be a threat.
You will probably see a lot of interest if you run a gith related game. Just a hunch.
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