> It works at first, but you end up wanting to design your own custom SSG once you run up against something that goes against your mental model of how things should work.

There is a middle ground. I hit this point in Jekyll when I wanted Insanely Great image thumbnailing that no extant Jekyll plugin could provide, ended up writing my own tool to do that, but didn't want to duplicate the rest of Jekyll's functionality too. It's kiiinda hacky and I probably should propose the interface changes upstream if I keep doing this, but a very light monkey-patch lets my tool pretend to be a Jekyll::StaticFile that just happens to write out many separate files: https://github.com/okeeblow/DistorteD/blob/master/DistorteD-...