Update the Application Detail view and List View to show a unified set of Badges (Deprecated, etc.), show PHIDs and Monograms on the Application Detail view, allow Applications to register Monograms.
Example of the page /applications/view/PhabricatorDiffusionApplication/:
Extension != application, although they often do.
An extension might only have Engine Extensions and stuff.
Also - maybe adding getPHIDclass() or getApplicationClass() to PhabricatorObjectRemarkupRule, and then running the search in reverse will make it easier for application authors?