Oh this would be so epic. I totally agree with ridd, forget the bedrock walls, make it a fully air map and paste some landscape in. You’ll get some people bridging off into the big empty, but it shouldn’t affect it significantly.
As to the nether: you could make it a totally empty world as well, meaning people would need to ship stuff through from the real world to build there.
Also, could you make people spawn randomly within the bounds of the ‘world’ like in the flatcore world? Just incase spawn gets lava’d.
Anyway, yes, this has my vote too!