> Take a look over some of the modules they're deprecating, like smtpd. What kind of standard library requires an SMTP daemon built in?

Just because it's not widely used doesn't mean it cannot be included in the stdlib. For instance, where I work, we have a MTA test framework that makes extensive use of smtpd to receive messages processed by our configured MTA which we then write to disk and subsequently make assertions on the message (e.g., contains certain headers, has certain recipients, etc.).

Having various protocols (client and server) in the stdlib is not a bad thing and, personally, I think it's very useful for testing purposes.