To expand on that, I was thinking about some standartization of sources (BUILD file in this case), standartize the way build tools could be plugged in, and also standartize the build outputs, so that they can be correctly included AND linked even without the sources.

Then you can build a lot of things on top of that, not only source sharing and automatic dependency resolver, but also remote build servers, sharing already built libraries to save time, and easier integration of various editors, IDEs and other tools.