This is a little wierd, but could we get an option to limit structure by structure the ability to spawn behind an achievement?
I recognize that this might be problematic with servers etc, who do you check for the achievement, etc, but this would allow progressive challenges and resources to be added to packs.

Can't you use the /#write command with command blocks to dynamically enable / disable the structure depending on the achievement status? I'd rather not tie that stuff to achievements.

Could we get a folder variant?

Folder variant?

I'd do it with structure tags and then moving all structures with tag x... I'll probably add it at some point, but currently it doesn't have a high priority.