There are two schools of thought. The first is that you should optimise for the platform you're targeting, so a fragmented JS world is a good thing because you optimise for different things depending on where your code is going to run. The second school of thought is that you should optimise for development, and you should have the same language everywhere even if that means slightly less efficient code.

For example, if you write long running services in node then optimising for memory allocation in order to avoid leaks is a good idea. It's less useful for clientside things that generally don't run for nearly as long. Conversely, if you write isomorphic JS that can run in the browser but also needs to run on the server for that first-load advantage, then you'd prefer if things work the same everywhere.

Neither school is 'right' per se. How a language ought to evolve is incredibly subjective.