The important part about breaking backward compatibility is allowing forward compatibility. Java is good in that regard, for each breaking change, you could sti

The important part about breaking backward compatibility is allowing forward compatibility. Java is good in that regard, for each breaking change, you could still create a library that worked for Java N and Java N+1. It is possible to have a network supporting IPv4 and IPv6. I don't think the speed of migration is an issue. It is not a tremendous success but it is not a failure either. In Python forward compatibility was often impossible. The migration benefit was low and the cost was high. Python is a great example how not to break things. I am little surprised that whole language is still popular after such failure of leadership.