“These updates will happen the same day they are available, so users don’t have to check in as often and sites are better protected from plugin and theme vulnerabilities getting exploited.”

I think that “same day” will prove to be a mistake. The next time a plugin with a lot of users releases a version with some fatal error that got through their testing (e.g. incompatibility with some other plugin, or specific old PHP version), automatic updates will mean that the number of people affected will be much larger. I’d have suggested that it be something like 2-3 days. That, of course, still means a larger window of vulnerability if the release was a security one – but these things are always trade-offs. (If plugin authors had the facility to tag their releases as security/critical ones that would help towards a solution).