The possibility of adding structures to a mod by using a vanilla structure block is awesome. You can control many options in the element editor, like the frequency, the biomes it spawns on and more.
But I think there still is a limit.
I think there should be an option like "check if there is enough space (air) for structure" or something similar. This would be extremely useful when adding a structure to a Nether-like dimension because it either spawns buried underground or floating in the air, never actually on the ground.
This would solve the structure spawning hidden underground or floating in the air, but I am not too sure about how does the structure find "ground" so it might spawn above bedrock. So I think there should also be an option to choose the height at which the structure will spawn or an option to blacklist some blocks so the structure won't spawn on them.
I'm sorry for my bad English