we have a proposal to add automatic updates to core, with the reasoning that it will allow rapid fixing of security flaws, and that is better than leaving upgrades to be checked by site managers on a testbed to make sure they won't break a site.
now its being suggested it may be worth adding further functionality that may increase security risks in core?

seems inconsistent to me - I'd leave this as a plugin. Editting the code is probably not a requirement for the majority of users, and for those that want to do it it'll probably be on a testbed machine anyway.