How to move objects from paper space to model space?

I don't know of one. I would reference the paper space into the model space and then merge the reference which will copy the objects into model space, then they can be deleted in paper space.

Why not change just your sheet model to a drawing model. You can do this in model properties or using model.type in vba.

This should do the trick.

Not sure if there's a key In (would love to know myself)

I haven't seen anything that will do that in one command (might be an interesting VBA project).

I usually just reference my sheet into my design, copy in the desired elements, Activate my sheet reference so I can delete the elements in question, then deactivate to get back to my design. It's not a single command, but it's not particularly complex, either.

I'm a few years late, are there any new updates on this subject?