So in my case the empty object would not be a few off-screen to track variables. Each image sprite would have an empty object parent. So there would be a LOT of empty objects moving around using behaviors and other plugins. I think that was the whole basis of requesting an empty object, to use as parents for a great number of sprites, not to use a few off-screen to tracks variables, etc.
The parent use for thousands of sprites lends credence to creating an empty object plugin for sure. Also, what SnipG said about the impact is interesting. With sprite invisible and collisions disabled, sounds like they are still in the render and collision lists and being checked against to a certain degree?
Reading everything again, I don't know if there are many projects (if any) that would be impacted by having a lot of invisible/collision-disabled sprites being used as an empty parent object. It doesn't impact my project at all BTW.