I don't play half-editions, so I would merrily be left behind in case of a revision.
I don't know if by "mechanical expansion" they really mean new rules or new character material, although in some cases (psionics) the two things happen at the same time. I would be happy in either case anyway. They might even consider a PHB2, DMG2 and MM2, although I don't think they'll have enough strong material for the first 2 of them.
As for the survey on Psionics, I must say that even tho I am not generally a fan, I found their second and latest design attempt quite impressive. I liked the system, almost all disciplines/talents/powers, and both subclasses. I am almost convinced I would actually welcome psionics in my D&D game for the first time ever... to actually win me, they just need a couple of otherwise significant improvements:
1- The base class is just too complex... you have Psionic Talents (basically cantrips), Psychic Focus (also at-will), and the Psi Points based effects (roughly corresponding to point-based spellcasting). And you get up to 6 different disciplines in the first 10 levels, meaning 6 Focuses and 12-20 "spells", plus the Talents. This is already complex enough for me and on par with PHB spellcasters, so I'd like that they simplify the rest of the class (there are 2 more abilities with their own mechanics to keep track of) or my players would probably not want to play this at all with too much stuff to learn. Maybe just streamlining the mechanics a little bit would help.
2- I would like the identity of "psionics = power of the mind" to be strengthened. For example, d6 HD and no armor proficiencies (just like Wizards, also based on non-physical powers). Some subclasses can reinstate those back easily, like the Order of the Immortal aka Psychic Warrior. In addition, I would remove those powers that grant benefits to other people, most notably the Adaptive Body discipline which is described as "augmenting your own body" but then lets you bestow resistance/immunities to others. This breaks my suspension of disbelief, but it depends on the actual effects (particularly, the really physical ones).
But overall I quite like this stuff... It's unique and different enough to hold as a base class on par with the PHB classes, both mechanically and narratively.