If WordPress has updates it would be nice to have email notices about these updates. On its own, not a super helpful or informative thing considering you should just log in regularly.
So I was thinking that WordPress should implement an "Update Status" which plugins can use to help classify the nature of their latest code. With this system it would be possible to then customize the before mentioned notices so only "Security Related" or "Critical Bugfix" updates generate email notices, and with that same system implement an Auto Update feature toggle allowing blog owners to customize not only which notifications they get but also which plugins WordPress will try to auto update.
I think something like this would really aid security and it shouldn't take too much doing to make happen. Even if the "Update status" system can't be implemented, a feature in the Plugins section allowing blog owners/admin to selectively auto-update plugins would do the trick pretty well too.