Babylon currently will parse multiple exports of the same name, though this should actually be a syntax error.

Here's the relevant portion of the spec and related Babel issue.

I'd love to take a look at and work on this! I currently have an open PR to the main Babel repo (where it was suggested that this change probably belongs in Babylon) with the modified tests. If/once this proposed change lands, I can update that PR to bump the Babylon version and fix the tests accordingly.