While the premise of the extension sounds like a joke, it's legitimately a good idea, and [one others have had independent of this][4]. I explain some of the thoughts and motivations behind NilPass's design here: https://nilpass.com/seriously/
[1]: http://www.cracked.com/article_18962_5-things-we-all-do-that...
[2]: https://github.com/nilpass/nilpass-branding/commit/6090b5cc9...
[3]: https://www.reddit.com/r/netsec/comments/62sgrp/presenting_n...
Not that this is not the case already, email accounts are already important.
Even if you use a different strong password for all sites, if a site offers a password forgot function your email account is still the weakest link.
I wouldn't try to encourage the broken "Forgotten Password" protocol... it's usually the softest target of authenticating on the web.