One of the stated goals of Go2 is forward and backward compatibility. We have to see how well this pans out when Go2 is released.
> Go 2 must also bring along all the existing Go 1 source code. We must not split the Go ecosystem. Mixed programs, in which packages written in Go 2 import packages written in Go 1 and vice versa, must work effortlessly during a transition period of multiple years. We'll have to figure out exactly how to do that; automated tooling like go fix will certainly play a part.