[photojosh]

I've wished we had this same concept of OS-provided base layer in other areas as well, where your app provides plugins that could be enabled in the core app. It came to my mind when Apple released their share extension method.

Maps: I use a few apps whose sole purpose is to provide location-based info (eg we have a govt app that gives fuel prices). This could just be a plugin layer that could be enabled in the Maps app. Property searches, your favourite fast food place, etc.

Camera: plugins could provide more effects or manual camera settings control UI, or indeed... AR overlays.