React, Flux, GraphQL, Hack, HHVM...? All of this and more!
WordPress is a popular CMS, but over the years the technical foundation of it has not kept up with the times. The UI remains top notch and Automattic has invested heavily in React.js and the WordPress Calypso content editing shell.
For WordPress the system cannot easily adapt Node.js as a whole since there is a large amount of existing tools and an developer base familiar with the worlds most popular CMS. This is why alternatives to WordPress written in Node.js is a common request, but there is no clear options at this time.
For developers some of the best Node.js CMSes as alternatives to WordPress are:
In addition there is a new option in the market: GraphCMS. This GraphQL powered CaaS platform is being Open Sourced to provide an alternative to Contentful.