Is it too late to make this a "+" thread? I remember how this went last time...but ok.
A lot of people need/want/prefer psionics to be mechanically different from spellcasting, but I don't really trust the current WotC team with that task. What's more important to me that it "feels" different, that psionics are evocative of forbidden, unearthly knowledge. The weird pulp Science Fantasy at the heart of early D&D. The City of the Gods. Expedition to the Barrier Peaks. The Derro, dear God, the Derro!
That there's something fundamentally wrong about "mind magic". Bring back Ioun sacrificing herself to wall off the Far Realms, where the source of psionics lays. Mindscapes and strange planes where one's thoughts and will shape reality.
Michael Moorcock-esque strangeness.
It's ok if it's spell slots and spells, as long as the powers themselves do odd things, and manifest in odd ways. Mentalists need not use any components (other than the "telepath stance", "the glare", or nosebleeds...oh yes, nosebleeds, have these powers actually cause strain to use, even if it's only a hit point or two, to get the message across that BRAINS ARE NOT MEANT TO DO THAT!).
A Wizard should see a Psion in action and be like "Dear Mystra! How are you doing...that?!".
That's what I want. But I wouldn't mind some psionic races. Gimme Blues, Derro Savants, Shardmindcs, and those cute Dromites! I'll even accept Elans, but I'm really EH about Kalashtar and Maenads (and Half Giants, who are only psionic because everyone is on Athas!).