> Bulletin board system gains nothing from "single page application" style architecture, it is a collection of documents, stick with it.

Real-time updates, differential updates, cacheable partials, free distributed rendering, to name a few.

Specifically in the realm of cacheable partials, every single site out there that repeats elements between pages could benefit as a well-architected SPA. It's analagous to h.264 vs GIF: you can compress/cache the similar chunks and only update the deltas and save bandwidth, making your platform more scalable. Sure, GIF can compress each individual frame, but h.264 improves on that dramatically by compressing in another dimension. The essence, in my mind, of the SPA is keeping your HTTP requests DRY.