Grey out the editor for excluded items

I often make the mistake to edit an item that's excluded. This happens for example when I make a backup copy of an item and then exclude it. Then I want to edit the original but often after about ten minutes I notice that I'm editing the excluded backup. That's annoying, time has been wasted and I've heard other people experiencing this too.

It would be really helpful if it's prominently visible that I've opened an excluded item, for example such as in this fabricated picture. The editing area is greyed out.