There are games that work with "two-button" joysticks as with the one on the C64GS, where the second button is activated by connecting Vcc/+5V to POTX. I don't know how difficult this would be to add as an emulation option, but it would be nice to have for the handful of games which support it. (Instead of rapid-fire button mode for "B".)
Some discussion of this in the VICE feature request tracker, with more info: https://sourceforge.net/p/vice…eature-requests/189/#ad94
Would this be interesting to users, and possible to implement?