The prototype site generator that I built to explore why Zola wasn’t working for me has now evolved into a nice little application in its own right. Documentation and download from https://hursts.org.uk/ssg, source code on github, if you’re interested.
Unfortunately, the directions it evolved in have taken it too far away from Zola to realistically fold it in as an alternative mode; the coding would be straightforward, but the documentation would be all but impossible.
A couple of features could easily and very usefully be added to Zola if the maintainers want to take a look. The [data] and [content] sections would make a really nice addition to Zola’s frontmatter concept and the sharding has also turned out very nicely, particularly when combined with loading from the [content] section. I think it works much better than my original markdown sharding idea.