You can still render placeholders from the server and fill these in with React

The more technical details you include the more people pick up and discuss minute technical details instead of the point of what I was trying to say, which is that my experience with a large codebase was these modern javascript tools have solved a lot of problems we had.

If you want all the gory details here they are: it was a Rails 3 app using Postgres and Elasticsearch that we migrated to React + node.js + webpack + babel, elastic search as the data store and using Keystone.js for backend data manipulation (which uses mongodb). Rails was indexing its data in Elasticsearch already so we could start serving data through node.js immediately without having to migrate all the data backend, which is being slowly moved to keystone.js.