I think you really need to differentiate between web applications and websites. Websites still are a lot better off with primarily static websites in terms of S

I think you really need to differentiate between web applications and websites. Websites still are a lot better off with primarily static websites in terms of SEO and performance (caching static pages is easier). For web applications a SPA approach definitely has advantages; for the biggest part in usability. Given that a vast majority of content on the web are pretty plain websites I'm sure Rails will stay relevant for quite a while longer.