I think this would be a nice idea.
I personally use Enhance's email service, but use Amazon SES as the outbound (smarthost). For me, it's working great. My emails are getting into inboxes.
I did have to configure the email server to use Dovecot's sieves (so i can filter incoming emails) and then turn on the sieve filter plugin for Roundcube, but now I have a fully-featured (excluding virus scanning) email set-up. Adam did tell me that the filtering side has already been logged as a feature request too.