One of the typical arguments in favor of small base languages is that frequently the best package will be written by a third party and become the "default", making the language bloated. For example, everyone uses Requests in Python instead of the built-in alternative. On the other hand, I think a big advantage of batteries-included languages that they define a standard implementation that other libraries can copy. Because there's an official JSON package for Go, everyone already knows how to use this new one, since it's a drop-in replacement. Obviously this won't happen in all cases, but when it does it feels really nice.

Looks neat, why not try to upstream it to the Go standard library if it's fully compatible?

My problem with serialization in Go isn't so much speed but marshalling/unmarshalling pain.

I've been using these packages with some success:

https://github.com/tidwall/sjson

https://github.com/tidwall/gjson

Not knocking this pkg, just thought I'd share xD

These dudes create some awesome stuff.

https://github.com/segmentio/nightmare

Now if there's a way to vendor built-in libraries...