[jpnelson]

By this argument, JSX shouldn't be published to NPM either.

You might argue that you know what you're consuming if you're importing, say, a React component, and it's likely written in JSX, but it's really a categorization issue.

A standard field in the package.json indicating what the source is written in might be useful, but would probably be left unpopulated. Personally, I find it fairly straightforward to tell what a package is written in just by looking at the source.