I think letting players get too close to the void is a bad idea, as mods may not behave well below y=0. Also players tend to build upward, not downward.
Although I'm not much fan of this idea at all, what if the SS were generated at Y=128 since the building limit is 256?
Other options could be:
- 2 new config options: where the station should be generated (ranges from y=32 to 128) and at where the player falls back to Earth: (should be always the former minus 1 and greater than y=1)
- an indestructible block but can be displaced via command or an item tool that make sures the player won't misuse it or break the station.