You are all thinking fairly close to the lines along which I was going.
Nussmier was close, but it got me to where I could find the Swappable Control Panels writeup (such that it is).
What I was considering was 3 different CPs, each with its own custom artwork, (Arcade Superstars, Air/Space Combat, Street Racer) that swap out with some manner of snap in/out solution.
Rather than use a separate encoder for each CP, I was thinking about programming one larger capability encoder for all of the various functions that would be in play for the games and accessories we have and then using a few multi-pin connectors (like the
http://www.mcmelectronics.com/product/DISTRIBUTED-BY-MCM-28-2195-/28-2195) to plug and play the desired CP. If the CP installed didn't have a particular function, that pair of wires would just be unterminated on that specific CP.
i would not need a 4-player option like the I-PAC 4 has, but the more programmable models that allow for 2 player clusters, plus a trackball, plus a spinner, plus a flight stick, etc would be the best for this configuration.