What about Super Action 4 button support? And Jag Pro Controller Support? And rotary controller support for Super Action Controller trackwheel? Finally, an excuse to mod a Jag pro to use all the buttons for Super Action Baseball and Football (both American and Soccer)
Also both use 12 buttons, 4 directions and one ground. The jaguar has 5 independent buttons, and 5 buttons that are remaps of keypad keys (pro controller) The CV has 4 independent buttons and 2 directions on the wheel. If you don't need the wheel, make the option key a program key.
A couple games don't work as Super Aciton games, and 2 don't work as standard games. Maybe there'd be menu option like 1=SA/Std 2= button reassisgn 3= keypad reassign (For Mouse trap, where you can use the buttons as keypad presses) 4= Joystick reassign 5= Rapid rwassign 6= roller on/off 7=SOCD Scrubber on/off 0=reset
on 2 you type L then R in Std mode or I,M,R,P (representing your 4 fingers) in SA mode in that order.
on 3, you type a eypad button and assign it to 1,3,4,5,6 for L,R,Z,Y,X on the Jag pro controller or C,B,A on gams that don't use and they swap positions for Mouse Trap, .
on 4 you can select W and E to be any 2 buttons for the Activiison Decathlon, or assign up to be a button on Smurf. Or you can flip a joystick 180 degrees for right-handed play.
on 5 first press button to select button to edit rapid fire, then press a rate with a keypad button where 1 alternates every "joystick frame", 2 alternates every 2 frames, etc. Start toggles always rapid on or off/ always held when held / rapid when held
There would be an RCA barrel cable either attached to the RF cable or the Composite/Component Y for the on screen display to interrupt or overlay on the game during program mode. Also would be used to confirm no rapid fire or SOCD Scrubber legal combination for tournament/world record play, or you can make option 7 SOCD scrubber on/off That way the guy who wants SOCD unscrubbed, and I can have it for Activision Decathlon.
Finally, is power only needed for rapid fire, or is power needed in the the adapter intrinsically. You forgot to include the suggestion I'd use for power: Rechargeable AA or AAA NiHM batteries (also compatible with Alkalines) That way if the batteries lose charge, just buy more rechargeable AA/AAA, not have a worthless brick unless you know how to replace the internal battery, AND find the part for it. I don't think AA/AAA will go out of style. Things meant to last many years use AA/AAA. Don't mess it up with a soldering job or an irreplaceable battery.