I did run a site on werc for some time in the past. After dealing with its particularity it becomes a great midpoint between having a static site and having a dynamic site.
Of course, in my view, it is always more preferable to have a static site in majority of individual use cases.
I would like to see more work put into engines which are static for normal users, but dynamic for logged-in users, e.g. the site author. It would be neat to integrate static site generation with dynamic posts, WebMentions &c.
Varnish is probably what prevents that nice thing to happen, by doing the same thing as NAT for IPv4: it works without rethinking everything.