A: Dennis, I’m sure somebody who saw a need for it, has made one for himself. Has anyone done so commercially? I doubt it. Hobbyists tend to concentrate on just one gauge, so there wouldn’t be enough demand to make it pay.
The challenge is your requirement to not interrupt the current. The center formation – usually called a diamond – on both Lionel and American Flyer crossovers was always made of Bakelite, a more-modern type of plastic, or some other non-conducting material.
This would have to be the case with your idea, even if you have a common ground for the two track loops. The two routes would have to be totally isolated from each other, with none of the rails touching. In addition, there would have to be at least a 1/8-inch clearance on each side, over and above the track width, to keep wide tinplate wheel treads from hitting something they shouldn’t and shorting out. This dead-zone center configuration would have to be made from hard wood or plastic and shaped in a way that allows the flanges to clear without the wheels dropping.
No matter how you slice it, this means that trains on both routes would have to jump a significant gap in electrical current without hesitating. I see no problem with most three-rail O gauge locomotives making it over what might be a gap of 1¼ inch (track width plus ¼-inch clearance) when crossing the S gauge track. Their wheelbases and pickup-roller spreads are usually enough. However, I’m not sure whether the shorter S gauge locomotives – particularly some of the diesels – could get across what might be at least a 1¾-inch dead zone over the O gauge track without a hiccup.
In any event, it could be an interesting project for you to tackle.