The argument for blocking outbound SMTP is not primarily about misconfigured servers. It's about malware that wants to send spam.
Nevertheless, in my experience, ISPs will unblock port 25 for customers on request. I've only worked with a few in my years, but I've not yet encountered any resistance.
Though it isn't always just inbound 25 traffic... often it's outbound as well. Also, the larger issue is hacked/pwned machines and bots, not just open relays. Which reminds me, I need to update Tomato on my router.
Issue with running your own mail server nowadays is spam. Gmail does a decent job filtering all the crap.