That's a super interesting idea; I was very into minecraft for a very long time (since 2010) and I ran servers for about 8 years, although they were mostly small community servers. We did a few interesting things like Skyblock mixed with a resource world so it was basicly making club houses in the sky, and a server that was nothing but ocean with islands. Nothing as radical as what you found though! My very last server was entirely a desert with one little oasis town.
Before minecraft I ran a bunch of super experimental servers in Blockland. One was like a world of infinite tunnels, and another was a world that was just an endless railroad and everyone travelled up and down it.
There used to be a lot of weird minecraft servers like that back in the day, but they got less and less common as players started just expecting everything to be hypixel; eventually it was just impossible to get players! Id suggest looking at the minecraft forums and planet minecraft forums (if they still exist?). They used to have server boards and the nice thing about a forum board is that its not based on upvotes or sponsorships, so you can see more unusual posts sometimes!