hi, here's a mockup I did for a few idea's for the Aero Studio program. But now Live 4 has pianoroll it might be worth considering
http://www.users.on.net/~edan/aero/pian ... ctrex.html
Now the key feature for me is INSERT/BACKSPACE to rearrange the notes, try it out (del=backspace). That combined with arrow key cursor control is awesome for rearranging tunes/beats super fast. The previewing scrub tool would be great for previewing chords.
Notice how a whole note/velocity/length and preview can be achieved before you even let go of the mouse button. Sounds should be previewing/triggering alot and sent through the pre-listen outputs. Pianorolls are so slow in most apps, I hope ableton can dare to do something better!
ps an option to map a virtual keyboard to normal computer keys is really handy especially for laptops.