I am interested to see what you do.
I have an X52 on order and when I get used to it was thinking about supplementing it with arcade controllers and buttons in a custom housing and a kade interface.
Seems simpler to use pre-existing stuff and customize it to me but I have been proved wrong far too many times.
I'd be happy to provide links for any of those parts, the major thing with what I'm doing is making the keyboard controller, that's software mostly, the hardware's almost all off the shelf and those arcade buttons are actually pretty popular with the home arcade crowd. Since I'd be making my hardware as a custom each time, I'd be able to use certain hardware as needed.
The thing stopping me right now is my finances aren't as good as I'd like, or I'd probably be doing a build log here instead of a survey and proposal.