I like the Yamaha idea 'one touch, two touch' ..... that should be universal, it just makes sense.

However, I still kind of like my big touch-pad idea for the reason of - I like to keep things as simple as possible. The fewer buttons the better..... the bigger (harder to miss!) the better! I feel (and probably anyone that had a drum machine in their old keyboard rig) that it's not that difficult to hit a button with exactly the same amount of control that you hit a key...... especially if they are big and soft enough (think MPC). I've seen a LOT of keyboard players lay into a drum machine pretty tastefully, no problem there with inaccuracy.

Aftertouch is another thing altogether..... I find that almost useless for triggering 'stuff' other than vibratos. It's just too hard to know whenever you might 'dig in' to the keyboard and inadvertently trigger the action. But velocity........ well, we use that on every key (61-88 of them!).

But I feel a lot of things could be simplified with velocity sensitive buttons....