I threw a proof of concept together to satisfy both our curiosity: https://github.com/staab/mithril-granular/blob/master/index.html
This allows you to call `this.use` in a component. It's not quite as clean as react/svelte, because it's less magical. The `onbeforeupdate` method is also a footgun as written (since it would prevent stateful child components from re-rendering), but that's an optimization anyway. Also see https://mithril.js.org/stream.html for mithril's own reactive solution. I'll have to give it a real try sometime.