Why not just use contentful (linked article is written by contentful) + static gen? My company has used contentful + middleman for almost 2 years now. It took a while to hone in (payloads used to be extremely large), but once it's dialed, the experience is better than WP for both writers and designers.
I haven't looked into it more than the five minutes surfing around after reading this article, so maybe I should look into it more.
It was hard to find info on their visual cms like editor in the few minutes I poked around Contentful's site. Maybe their CMS like editor is really simple/similar to wordpress I will read some more.
Another quick thought is wordpress has a huge amount of plugins that these non-technical clients are used to, so probably some retooling would be needed to reproduce what they want.
I have no problem creating and updating static sites myself so the only need really is to provide clients a way to add content and mess around with site through a visual cms (e.g. use a visual editor plugin to add new slideshow type content and change layouts).
Without wanting to plug my own software too much too soon, I've been building a self-hosted static publishing CMS (that sits on top of a git repository rather than a database). Not ready for prime time just yet, but getting there
