On the Santana tandem we had, years ago, one brake lever worked BOTH the front and rear cantilever brakes -- two cables coming out. The other lever worked the drum (drag) brake for controlling speed down hills.
There is no problem on a tandem with the bike flipping if the front wheel locked. It wouldn't happen. The pads would tend to wear evenly, too.
I would not try that set-up on a standard single bike. Might work on some recumbents.