The only trouble I have with the A4 is the two-hand track muting, when I have to tweak some knob at the same time, for cool transition effect for instance.
I know many people have already mentionned it, but here is my idea :
Why not inverting track mute and track selection when in performance mode ?
I mean you can mute/unmute with direct track keys on the right, and select a track with function+track keys.
I could find tons of other changes, like everything possible with DSP + analog hardware, and like the things you mentionned before, but actually I really like the - relative - simplicity of this piece of gear... It makes it very musical to me.
And even in that OS state, I'm sure I can only see like 1% of its capabilities