About a year or so ago I made the large Multi-Platform system, which, let's face it, was quite big, clunky and looked like a cake (as my wife put it).
At that time, the system was made that size to take the larger console boards, after all, I wasn't into chipping up boards and relocating sections at the time. I also used two multi-cart ports from N64's to connect power, audio, video and button presses between the two sections, so in effect, one half of the system was the screen and controls and the other half the console itself. It worked fine, but cumbersome.
In the forum, someone was talking before about clipping on a PSone screen onto unmodded consoles and connecting the two by a serial cable, or whatever. I suggested he might consider using magnets and metal pieces to keep and maintain contact between the units, so as to not have unsightly plugs and wires; also the magnets would help to keep the system held together. Magnets by their nature are conductive after all. As the magnets will be slightly recessed in 2mm perspex, they will not have an electrical impact on the rest of the system (careful placement).
My idea, which I will experiment with now, is to cross the two design concepts together. My existing case top is big enough to take a PSone screen, two speakers, d-pad, 4 button pad and two joysticks; about 21mm thick so everything is held inside and flush. The bottom section is good for up to about 33mm or thereabouts; which is fine to hold a console board, batteries and cart / CD section. This means my existing casing is up to the job; at least in theory.
This got me thinking.
If I were to make the two sections entirely separate, with a bank of magnets around the case perimeter, that would hold the two case sections together; especially if the screen section was slightly recessed and the console section slightly inclined; to stop the two sections sliding apart. The magnets and steel metal (on console section) would communicate the power, audio, video and controls; and also keep the sections together.
This in effect would give a major version 2 upgrade of the Multi-Platform system - much smaller, easier to hold, interchangeable, vacuum formed, colourful and sleek.
I therefore intend to do this, now - starting with my TurboGrafx. If successful, I will make an N64 section too for it; then announce the finished project to various sites. Two systems is a good idea (or even three) so people can see the concept working properly. This also means more production time before a release!
The issue with needing extra buttons is solved as such: two joysticks is all you need, if that for consoles, some use d-pad, all use buttons. If a system needs more than four buttons (eg Gamecube, N64) then they can be mounted under the case. If you think about it, shoulder buttons on a console are far easier to use if under the case, otherwise you need to move your fingers about; using the C buttons on an N64 controller is awkward anyway for the same reason, so why not have them under the console anyway? That way, you can press all the buttons without adjusting your grip of the console unit.
Thoery is sound, and I know I can do it; although I will need to experiment to see how viable it is in practice. If I can pull this off, it will be truly awesome!
It will also mean I have a glut of spare PSone screens too! 
