This is not recommended practice because it won’t scale, but “hear me out”. 
Both Vue and React can be used without transpilation or build step. This means it can also be used inside Yii widget code to give some “reactivity”. Did anyone try this? Vue can use its template directives, like v-if, v-for, etc, and React can also compile JSX with Babel inside the browser. Again, it won’t scale good because performance is always better if you precompile and bundle the JS, but maybe it could be useful in some situations?