[crabmusket]

This seems to be exactly how Gatsby et al work, by pulling in "dynamic" content over an API at build time. I've never seen this being used to re-render a site based on third-party changes like comments, but it's popular to pull data from a first-party system like a CMS containing e.g. the blog posts.

Though I wonder if the prevalence of programmable edge networks will leapfrog that before it becomes really mainstream, and allow site owners to add a small bit of edge dynamism to pull dynamic content in without client-side JS.