This seems loosely equivalent to Google's account activity mail, but with invade-by-default. I can see it being useful, though, despite the flaws which you desc

This seems loosely equivalent to Google's account activity mail, but with invade-by-default. I can see it being useful, though, despite the flaws which you describe. Also – potentially – incredibly dangerous, as other posters mention. I don't think that we can have the possibility of one without the possibility of the other here.