I like the idea of a nav cluster in the middle (I've been playing around with that myself with a macro pad between the halves of my splits), but I agree with another commenter about BNM being wonky. I love "left" and "right" as layer names; I wish I had thought of that! It makes a lot more sense than "raise" and "lower" if you've got the MO switches on separate sides like most builds seem to.