The Ardent and Divine Mind are already pretty leader-y. They work with auras and I can see that as the Big Thing that psi would utilize for its own schtick.
So let's theorize.
The psion (controller role) would have your basic will/encounter/day powers, except his encounter powers are all auras; they last for the entire duration and you can use only one aura per encounter (see also: channel divinity).
The psion would have destructive powers.
Psionic Aura: Unravel Thoughts Psion Attack 1
Encounter * Psionic, Psychic
Special: You may use only one Psionic Aura ability per encounter.
Standard Action Personal
Effect: aura 5; enemies that enter or start their turns in the aura take {Int modifier} psychic damage.
Ardents would have beneficial powers.
Psionic Aura: Intellect Fortress Ardent Class Feature
Encounter * Psionic
Special: You may use only one Psionic Aura ability per encounter.
Standard Action Personal
Effect: aura 5; you and allies that enter or start their turns in the aura gain resist psychic 5 until the end of their next turn.
Or something. Just thinking out loud here.
EDIT: Soulknives seem very well suited for Followup attacks. First they stab you in the gut with their Psylocke ripoff manifestation of their will and then they bombarding your nervous system with overload, or erasing memories, or hijacking metabolic functions. I predict Crisis of Breath shall see a return as a soulknive Followup that essentially says:
Wis vs Will, ongoing damage 5 (save ends).
