I was wondering if it is really necessary to copy all of the template folder's contents to a new sub-template folder when creating a new sub-template. Online instructions seem to suggest this is necessary, but it can be burdensome when upgrading between versions that have template changes. Does anyone know if I can just copy, say for the example the item.php file and leave out the rest. It would then simply default to the default files.

If not, this would be a desirable feature.

I think it will work as you expect. Copy the one file and give it a go

Yup. It worked fine.