Having read most of the intervening pages, I have been swayed strongly to "Psions should be able to do anything magic (wizards) can do". I think, however, that Psions (like druids or my ideal of sorcerers), should stay strongly or entirely within their "Disciplines". (I did that same effort for Clerics, once upon a time for 3e.) So while a "Psion" should be potentially be able to throw a fireball or raise the dead or accomplish a wish, those three examples should take a Pyrokinetic, a Psychosoular (yeah, what word would that be), or a Portalpsi (another "what's the word").
If you, the Psion in question, don't have pyrokinesis, you aren't throwing fireball. But if you gained and trained it, maybe. Potentially - complicated sub rules - with limited crossover. Like a Telekinetic might be able to "fake" all the energy-kinesis at 2 (or more!) levels weaker, or some other creative mechanics (like scooping up flame from a bonfire and hurling it at foes, but not the actual creation of a propelled 20' radius fiery grenade); the portal specialist might open a portal to the elemental plane of fire, and allow a gout of flame to burst forth... but that still isn't the perfectly controlled bead of explosive combustion force the pyrokinetic is achieving.
On the other hand, the portal guy can open a portal to Elemental Air and trigger a gust of wind, while the Pyrokinetic is pointing at the backblast of air after the explosive combustion and hoping that counts. The telekinetic can lift the boulder, but the pyrokinetic is blasting it out of the way, or blowing it up. Telekinetic flight, pyrokinetic "rocket jumps".
