There was no chance that everyone would be running their own email server, but if it wasn't for the lack of IPv6 adaptation a plug and go home email server solution would probably see a decent amount of use. I'd bet we'd already be seeing it as a feature in most mid-ranged home routers by now.
For one, if my power goes out for an extended period of time I'd still like to be able to access my email. Communications really can't be hosted locally.
The mail server in a router is easy to host, the problem is:
1) Uptime (though this could be partially alleviated by retries)
and most of all:
2) "Trust"/"Spam score"
It's the main reason to use Sendgrid, AWS, Google, etc. Their "value" is not the email service, it's that their SMTP servers are trusted.
If tomorrow I can just send from localhost instead of going through Google it's fine for me, but in reality, my emails won't arrive due to these filters.