Google has released its Contacts and Phone app on Google Play today thereby allowing them to be updated independently of the OS. The apps only seems to be available for download for devices running Android 6.0 Marshmallow though.
The update to the Phone app introduces Call blocking, a feature that has surprisingly been missing from stock Android until now. The update to the Contacts app does not bring about any new feature, though its change log does lists a more streamlined layout for contact editing and some bug fixes.
There does not seem to be any other changes in either apps, but now that Google has decoupled them from the core OS, they can at least add new features to it without pushing a whole update to the OS in the future.
Update: For some reason, Google has pulled the apps from Google Play.