It's a traditional web app, so it works with HTML. We don't plan to have anything else any time soon so the priority was on the time to have the HTML ready to go.
I did a Rails app serving JSON exactly one year ago, to a small Angular front end. It's was a little disheartening to see an empty page loading and then making JSON calls and thinking that by then a server rendered page would have been already fully loaded. That's why I said that it's all or nothing: either a single page app or many html pages. A few single app pages don't do well, unless they are preloaded with server rendered content.
I did a Rails app serving JSON exactly one year ago, to a small Angular front end. It's was a little disheartening to see an empty page loading and then making JSON calls and thinking that by then a server rendered page would have been already fully loaded. That's why I said that it's all or nothing: either a single page app or many html pages. A few single app pages don't do well, unless they are preloaded with server rendered content.