Better composition and code reusing are top important topics of modern front-end development. Great solution for this is web-components technology but it requires few polyfills in order to work properly in modern browsers. This impacts performance and reliability. ReactiveElements allows to use React.js for web-components definition, avoid including most of polyfills and build project with web-components right now.
UPD: You may use MVC Elements in order to create Web Components of Angular and Backbone views.