It'd be nice to be able to automatically load/compile/execute es6 scripts in the browser (sort of like require('6to5/register') in node).

<script type="text/ecmascript" src="node_modules/6to5/browser.js"></script>
<script type="text/ecmascript-6" src="app.js"></script>

The use case I currently have is being able to open a test runner in the browser without needing a build step. Or rather, refreshing is the build step.

Coffee-script and Traceur support this (along with others).