Very Good ISO performance would be an upgrade for me (assuming that means at least one and possibly two stops lower noise)
That's a very optimistic interpretation of 'very good ISO performance'. A full stop improvement would be a significant jump in technology (especially if it was a 24 MP sensor). Two stops would be groundbreaking. Not going to say it's impossible, but making a crop sensor with better ISO performance than the best full frame sensors would be huge, and it wouldn't be premiered on a $2000 camera.
Given that the 7D has about 40% QE, a 2 stop improvement of the (photon) noise would mean 160% QE, enough to earn Canon a Nobel prize, and shake the foundations of physics.
I don't need them to find new physics and win a Nobel Prize (I wouldn't complain if they did) but getting rid of that annoying banding noise the 7D sensor produces would count almost as much for me