Correct this is about attacks against user accounts not legal requests. We do notify users wherever possible about legal requests and statistics are in the transparency report:
https://www.google.com/transparencyreport/userdatarequests/l...
In that vein, end-to-end would protect those users even if you can not alert them. Your hands are tied with something like PGP because you couldn't access it even if you wanted to. Someone mentioned your end-to-end extension. Will you be releasing end-to-end to the Web Store soon? Or some other killer end-to-end solution?