I was thinking just now what if windows 8.1 had mode called paper mode? Think about it, we have our tiles we can change color, we have our monochromatic mode, but if we have paper mode like pebble that can help with battery life.
Unless I completely misunderstand what you're saying, the Pebble watch doesn't have a paper "mode", it has an e-Ink (or E-Paper) screen - same as the Amazon Kindle. So Windows PHONE 8.1 can't have a 'paper mode'. Of course handsets could have an E-Paper screen - but for a smartphone that would be pretty dumb given the slow refresh times for this type of technology (ie. no games, no videos).