HN user
Looks interesting. As for the password hashing, have you tried the one built in to Werkzeug? http://flask.pocoo.org/snippets/54/
Btw., I have a similar project (with a much smaller scope) at https://github.com/codenhagen/startflaskproject.
iCloud Keychain can be used offline (although it doesn't work with other platforms). https://support.apple.com/en-us/HT204085
How well does it work with iOS/Android (I know OP didn't ask about mobile apps, but I'm curious)? The page says that there are apps available, but those seem to be the kind of apps that are a pain to install.
Just tried out the developer version (http://www.opera.com/developer - built-in VPN and ad blocking is currently only available in the developer version of Opera). Both the ad blocking and the VPN works great in the few sites I tested. I especially love that turning the VPN on doesn't require any type of login.
Also: Mandrill.