That's a really good idea, Ninjis.
Possibly a breakout box/hotsync cable, allowing the user to plug in whatever controller that they want to use.
(NES, SNES, Genesis)
Let's break it down a bit...
Standard Nintendo NES Controller ($0.99 Gamestop)
The NES controller has 8 buttons.
(Up, Down, Left, Right, A, B, Start, and Select)
The GC10 has Up, Down, Left, Right, A, B, X, Y, and I think a hold switch. lol, I don't have a gc10 yet. If there are more buttons on one of these, let me know. ^_^
So NES, is definitely workable. ^_^
Standard Sega Genesis Controller (db-9)(3 btn) ($0.99 Gamestop)
The STANDARD Genesis controller has 8 buttons...
(Up, Down, Left, Right, A, B, C, and Start)
So, it's do-able as well. ^_^
The 6-button controller would probably be unusable, except as a 3 button, (the default setting) allowing all 6 buttons to work would require detailed information on what happens inside the Genesis, AND inside the software after you push the "Mode" button on one of these. Work on the 6-button could possibly lead to the....
Standard Nintendo SNES Controller ($5.99 Gamestop !OUCH!)
The standard SNES controller has...
(Up, Down, Left, Right, A, B, X, Y, L, R, Select, and Start)
This monster has 12 buttons, 4 more than either the Genesis, or the NES.
Now it gets funky.....
The standard Sony Clie GC10 drivers should be able to work very well with NES, or GENESIS Controllers.
Now, the interface for a SNES controller is definatley possible, BUT the software required to read those 12 buttons is probably above the Stock Clie GC10 software's "comprehension".
(I'd almost bet on it. ^_^)
So, in order for the SNES to FULLY work, it'll take a Palm OS programmer, to write the code for the interface. ^_^
(Big plus if this happens, NO SONY SOFTWARE REQUIRED

)
So that's where we stand, the NES, and Genesis controllers shouldn't be a problem @ all.
The SNES Controller will require software beyond what the GC10 drivers can (Currently) do.
To sum it up. ^_^
Order of difficulty to successfully pull off.
(10=Easy | 1=Not impossible, but OMG!!!)
NES=10
Genesis=10
SNES=4
Genesis 6 button=1
AND this isn't counting diagnols, which may require more software, depending on if the GC10 can recognize 2 directional buttons being pressed at the same time.
Whew, lol.
I'm personally hyped up about the idea of playing Zelda, and CastleVania2 with an NES Dogbone. When Genesis emulation on the palm OS gets there, then this device will be ready for it.
Thoughts, Idea, Suggestions, and Whims are welcomed. ^_^
Keep 'em coming. ^_^
Thanks!
84Mouse