If making a modular or swappable panel, just using interfaces that have a USB connection should be sufficient as you just unplug the cable from the interface mounted on the panel and plug it into the interface on the swapped panel.
You mean having a separate keyboard encoder for each panel? That'd get spendy.
I think it would be better to have the encoder stay with the cabinet and have all inputs wired to a connector that connects it to the panel. I think people have used printer cables for this in the past.
I considered swappable panels when I did my first machine, but then decided I would rather have multiple games... I ended up with a horizontal a vertical and one with a dedicated Stargate layout that will also work for Defender and a bunch of other 1 or 2 button games.