I like the idea that our open source approach must evolve. However, I'm not entirely convinced that moving to a contract approach is the way to do this - after all, one of the largest reasons that open source proliferated these past few decades is that it offered a range of both copyleft licenses like the GPL that promoted freedom first and foremost, as well as a wide range of permissive licenses like MIT that promoted code adoption in other (possibly commercial) projects. Thus, a contract approach would likely require a wide range of complex contract types, and this may dissuade adoption.