I'm probably going to make a Wico conversion this weekend. Last weekend I realized a cool way to replace the cable without cutting up one of my 9-pin extension cables or a Genesis controller. I'm going to put a D-9 female into the housing of the joystick itself, then the extension cable can hook right up to that.
What I also think the CV needs is better controllers. The controllers just don't make it fun for me to play it.
I know it's possible to rig up the two buttons to either Coleco or 7800 mode, and wire the switch to swap them, but I don't think it's possible to do both Coleco and 7800 mode without adding another switch.
Then of course the remaining problem is the keypad. I have a pair of Champ keyboard controllers, but I traced the circuit a couple of years back and the pass-thru port is wired to not pass the second fire button. Maybe I'll put make a Y adapter box or put a pass-through port on a Coleco version of the Wico conversion. I have a couple of Y cables somewhere, but they're 7-wire Y cables, so those won't work.