> I've seen some commercial keyboards like this, but they're incredibly expensive and non-mechanical (mostly geared to people who are disabled/have limited or no use of one hand).

The Matias 508 is one such http://www.508keyboard.com/ , are there others?

One feature you might want in such an arrangement is a capactive sensor in the mouse: https://plus.google.com/105224327306964621564/posts/51Jkbioc...