What we are trying to achieve
Thinking about SEO
Having worked in SEO for years, I am somewhat of a Don Quixote fighting websites that won’t render when you do not have JavaScript capabilities. I am a firm believer in progressive enhancement, ensuring that the core of the website is functional when you disable CSS and JavaScript. Whilst we had to make some concessions on this principle during the development of this project, I kept in mind that search engines can view the site also.
Yes, we are aware that Googlebot is evergreen nowadays and yes, we know of its JavaScript capabilities. Yet we are also aware of the delay in queues when it comes to processing JavaScript...
The fact that each page operates without JavaScript and crawling software, such as Screaming Frog, shows that every page can be found and crawled - without the use of a static HTML/XML sitemap. So that is good.
Additional benefits
When thinking about page speed and Single Page Applications (SPAs), you don't want to end up with a loading screen showing a loading indicator while the SPA initialises. You want to show the user the content as quickly as possible, and then have the scripts begin to take control.
In short, by ensuring that the initial server-to-browser transaction features enough payload to show initial content to the user, both page speed and user-experience will benefit. With the isomorphic framework taking over the consequent loading journeys, this reward is only enhanced.