deskthority

I feel that straight keyboard only works if the halves are physically split.

Looking good! You're quite right about programmability freeing you from too many hard commitments: the only thing you have to decide at the outset is the size and position of keys; not their content. You've got a nice one in the works there.

Symmetric stagger is always at the back of my mind, too ...

What about symmetric stagger?
Here's a prototype I sketched:

http://www.keyboard-layout-editor.com/# ... 695b685cac

(I didn't really think the labels through, but if the keyboard is programmable it'll be easy to swap some keys around )