There is/was a vote on this pretty soon. We are deciding how modules would work - with a new file extension? With a module.json? With a separate entry entry in package.json? Lots of decisions to be made :)
Any solution that requires extra work (file extension, another file to maintain) is a non-starter.
Frankly it should work how Babel transpiles it - because there's no reason for it not to.
Yet they were solved for that.