Re DB15, It's certainly possible but I'm not sure why it would be needed? If the pass-through were being utilised in a cab the cabs controls would be utilised, and if it were used in conjunction with a supergun surely the supergun would provide its own controller inputs.
I've thought it would be neat to have a way to connect to PS4 controller or any wireless controller.
Hey I was thinking have you considered making Jamma cabinet linking sets?
I think their could be a few people interested in these if they were made well. I was thinking of making one but as I'm a noob at this kind of thing it would be awhile before I could do it myself. The idea is to use a modified jamma pass-through at one end that includes a connector for the Video and one for the player 2 controls. At the other end would be a similar board without the jamma connector. The idea would be to use standard connectors like VGA for the video and a 12 pin din plug or something for the controls. Would be nice to use some standard cable that has the correct number of cores but I can't think of one of the top of my head. I guess you could just use a header or something and people could crimp a cable together.
Just an idea as I have seen ant quality Jamma link setups for sale and its seems relatively simple in construction, specially if generic cables can be used.
Cabs: Namco Noir x 4, Namco Noir Clone x 2, Namco Exceleena x 7, AW Super Sports Shooting USA,Time Crisis II 2P, 6P X-Men, Battle Gear 2 2P and 4P Gauntlet. My partner is not impressed.