So for now this is just an idea so keep that in mind.
A few years back I looked into a project that would make a USB adaptor that worked with ALL controllers for ALL systems (aka unicon). The idea fell through, mostly because I wanted to make a product and the cost of connectors for the various systems would just make the whole thing impractical... not to mention the fact that I'm a novice at AVR programming.
Well things have changed since then. The arduino has hit and now you can find source code examples that aren't all assembly (which reads like stereo instructions to me). In addition we have stuff like 3d printers and cnc machines, and mail away pcb manufacturing, so some of those hurdles aren't as big now.
I stumbled across a nes/snes arduino sketch yesterday and it actually used an auto-detect method I mentioned in the old thread.... it works well. I also found a sega Saturn sketch that works and proves to me that timing is inconsequential on the sega multiplexor chip. That means I can do some shady stuff like wire two sega gamepads to the same connector and power one on at a time and read them... meaning I can run two sega gamepads on 10 pins instead of 18.
The Saturn protocol is the same used for the genesis and mastersystem and "sort of" the same for the Atari vcs and "classic" systems. The NES/SNES protocol is also used by the virtual boy. So if I write my own auto-detect code and combine these two sketches that'll cover the master system, the genesis, the Saturn, the 2600, the c64 and all those oddball systems, the nes, the snes and the virtual boy. That's a pretty good start! If I modify things slightly, I can also add neogeo, which is just genesis with more pins instead of the multiplexor. The tg16 has a different button layout, but it uses the genesis protocol as well.
I'm going to work on it when I get a chance to sit down. I already have some snes connectors lying around. Sega and classic consoles just use a db9, which I also have lying around. You can actually buy nes connectors at this point for 2 bucks a pop. So I'm going to sit down and see what I can come up with.
N64 and beyond requires "bit banging" which is just as scary as it sounds, but this early stuff.... yeah I think with the examples out there I can make something.