I am currently building a static-file blogging system based on Prismic.io and Middleman. It's going pretty well.

The hardest part is that we are going to have a build server that rebuilds the stale parts of the site every hour or so - I don't think that's been done with Middleman before, so we're building that from scratch.

I'll post the details on https://tech.bellycard.com when we're done with it.