[2020] Is it technically possible to autogenerate an "all underground" map?

Well, it is definitely possible to make terrain blocks not collapse.

It may be possible to move original player spawn points underground (not sure if that actually works) but features like "spawn near your bedroll" would require code changes to allow spawning underground for sure.

What I am wondering is... how interesting would the game be without the 7 day horde, without wandering hordes, without biome spawns.