Editing the keymap to achieve what is wanted here is *really* trivial, like...really.
The ideal place to start if you want to get your feet wet in the Rockbox source/compiling.
User-Configurable keymaps (in core) isn't going to happen any time soon, and it's even less likely that the default keymap would change IMO, it's been a long time coming and many discussions to get them into the state that they are now.
[St.]