Both setups look like they would work. The battery issue will always plague good ideas such as these. Going with wires would be impossible, so it would be good if they could put rechargeable batteries in them, and have a small plug to charge them after a few days of riding.
IMHO flashing or pulsing brake lights would be the way to go. There are several vendors out there that offer them, but placement of extra brake lights has always been the issue.
Not to get off topic:
I ran across a car hauler a while back that had turn signals on both sides of the trailer that flashed 4 times then blinked in sequential order like the turn signals on an old Mercury Cougar. Caught my attention real quick. They were LED's and they were bright.
I haven't been able to find any online yet. They weren't that big, and they looked like they would fit in the back of a hard saddle bag, or with a little fab work, add them to either side of the fender.