brian85 mithril is such a lightweight/fast library (not really a framework), there's really not much to learning it. If you are familiar with JavaScript and optionally JSX at all, you are already almost fully prepared to jump into developing frontend.
At first glance, a flarum component isn't all that different than a react component. There's only subtle differences in lifecycle methods and state.
React:
export default class ReactComponent extends React.Component {
render() {
return <h2>Hi, world!!</h2>;
}
}
Flarum:
export default class FlarumComponent extends Component {
view() {
return <h2> Hi, world!! </h2>
}
}
Underneath the surface, can you honestly say that Mithril is stopping anyone from developing for flarum? Even passing props to components are handled in a similar way. If anything, requiring Vue would just introduce more of a learning curve for people unfamiliar with the Vue framework.