Bitte melde dich an, um diesen Link zu sehen.: in principle a nice idea, but that wouldn't be "original" anymore.
Also since there are not that many 4-Player games for the c64 (paddle games don't count) it would be wasted resources from my point of view.
On top of this comes, that there are several adapters out there: Bitte melde dich an, um diesen Link zu sehen.
So which one should be implemented ???
I would say, leave the choice, which 4-Player adapter to use with the user
and that's, why i absolutely prefer, having the Userport working (be 99.9999% c64 compatible), because than i can plug in, whatever was in my c64 before. Centronix interface, 4-Player Adapter, etc., etc.,... .