What about the downriggers that can follow the contour of the bottom using a depthfinder, keeping the ball a pre-programmed number of feet above bottom? If they could figure out a way to deal with the reel taking up the slack when the ball rises, that would be a pretty good upgrade.
I realize it's not a new system off keeping a bait down, but still an improvement.
BTW...I love downriggers, particularly since I went electric. (and I love flyfishing)