My cork popper would have to include:

61 solid keys
quality speakers
ample buttons for real time access
instant access to volumes for parts
hard drive support
quality mic in with user definable harmonizer
manual bass in a flash
arranger in a flash
logical style progression
tasteful, understated fills (generic)
no touch screen ... or at least - buttons that duplicate the screen's.
under 40lbs....preferably under 35.
no wasted space to the L & R of the keys
(Tyros & VA7 have SO much space there)

I don't expect all these items to be produced in the near future... it seems that the touch screen is coming of age. I hate it, but some seem to respond to it. It's awkward and clumsy in a live rig, and I'd love to see it gone.