They never went away, it's that they were in the design process of the new board plus negotiating with the DCC folks. Took a while but now they've come out with the new board that, depending on the one you pick, is more suited for large-scale such as our O-scale engines.
Even with battery power, you don't "need" to do away with the 3rd rail, although there's no need to have it once the conversions are made to BPRC. I ran my BPRC fleet for a while before I removed the middle rail, then eventually tore it all out and rebuilt using code 148 2-rail track and Mianne benchwork. I still use 3-rail wheels, but on the engines and passenger cars I've removed the center rollers.
I'm playing with battery-power in my passenger cars now. I know it works because I've done 2 cars, but finding a place to put the charging jack has slowed me down. Using the track to charge would be wonderful, or better yet a conductive charging system (think cordless toothbrush) would be great. I even drew up a water column design so the charging cord would coil up on a spool underneath it, but the drawing is as far as I've gotten. Simply pull it out and plug it into the jack on the engine, when done it should retract on it's own: