I hope this works out. If enough of the big email vendors (gmail, outlook, yahoo, etc.) get on board the network effect could be enough to push adoption to a very high percentage.
Once that happens my "unencrypted" email folder would be viewed about as often as my junk mail folder.
And then... maybe just maybe... spammers will be faced with a serious challenge.
It'd probably become like SPF/DKIM - somewhat spammy companies who still have a genuine mailing list and will still opt you out if you ask (or even click 'Spam' in gmail etc via FBLs) will go to the effort to implement it, but random viagra spam being pumped out by botnets likely won't.
They'd just keep creating new keys, and use a botnet to exchange seemingly valid e-mails with itself and a trickle of seemingly legit e-mails (buy access to a few small legit mailing lists to make sure their botnet isn't a total island). It's not clear to me that this won't make it possible for spammers to manufacture/buy sufficient "trust" to put themselves in a better situation than they're in today.
Once that happens my "unencrypted" email folder would be viewed about as often as my junk mail folder.
And then... maybe just maybe... spammers will be faced with a serious challenge.