I'm curious as to why yarn instead of contributing to NPM? I am aware that yarn was the inspiration for many improvements for NPM by providing an alternative, but going forward do we need two systems? Is the plan for yarn to be compatible with NPM and package.json?
I've been using both for a while and I'm happy with their decision not to try and be "compatible" with NPM. I'm also pretty happy with using Yarn only - things are just faster and in reality make a little bit more sense.