I definitely think there's demand for solutions like this. I probably would like this even better if it worked on top of an existing static-site generator platform like Jekyll or Gatsby.

I just wrote about immutable deployments with Ghost 1.0, which is also open source (MIT licensed), and how that can be a nice compromise between static sites and hosted CMSes: https://ryanashcraft.me/ghost-and-now/

I might've tried Publii out if I had heard about it beforehand, but right now I'm really happy with the entire Ghost editing and consumption experience I've set up (thanks to the Ghost and Zeit teams).