Long ago (like 3-4 years ago) I had the same idea but writing such a thing as apache/ngnix module with lua. However the effort require would've been tremendous. But now there's fuse. Also it predates module systems..so in some ways it was easier on the requirements side. However I think even with all the new requirements it is theoretically possible to write such a tool. Advantage is that it would throw complexity of ordered fetching and in-browser transpiling etc.
Can think of at least two - 1. It throws out the additional complexity of managing order of JS execution. Things are much easier on node.js. Just look at my systemjs-emulator...it's hardly 200 lines (without the plugin API though). Browsers have so many quirks I guess. and 2. avoids any in-browser transpiling.
^ It is still a guess though (I think it will reduce code complexity and manageability). Not worth working on the tool if that turns out to be false.