User perspective:
If you want something big I’d pitch nixos. As in the core distribution. It’s a documentation nightmare and as a user I had to go over options search and then trying to figure out what they mean more often than I found a comprehensive documentation.
That would be half writing and half coordinating writers though I suspect.
Another great project with mixed quality documentation is openhab. It fits the bill of more backend heavy side and the devs are very open in my experience. I see it actually as superior in its core concepts to the way more popular home assistant in every aspect except documentation!
That said: thanks for putting the effort in! ♥
If that’s your intend than it might be better to pick individual arch wiki pages or improve the entry documentation. Many people refer to there from all distro because of its volume.
A “how to read tech documentation” could add value for this target group.