I myself have been working on https://starthq.com which started life as a single page app using AngularJS where most of the functionality was behind a login. It has now pivoted into a web app directory, where delivering the initial page quickly and in a way that Google can easily index is crucial & there's very little actual input validation or interactivity on the page. The nice thing is that despite this transition, the core API has remained the same regardless of where the view is rendered and the architecture is all the better for it.
Give it a go and see if you can tell which pages are rendered entirely on the server and which entirely on the client.