What is the feature you want to see?
Make the E3 Demo dimension get generated using structure files and /place

Why would you like this feature?
This makes it much easier to install the add-on.

Any alternatives you've considered?
Jigsaw generation; but the rotation cannot be set using /place, and they cannot otherwise be triggered. They also have a limit on how far out they can spawn templates.

Additional context
The overworld is able to be /clone-d to the original mansion. /clone from minecraft:overworld X Y Z X Y Z to e3_demo:original X Y Z; this should not be done for the mansion rooms, only the Boo Woods.