Application level willInsertElement event callback without views

The purpose is to remove placeholder content when an application loads, so ideally it should only fire once on application load. In the olden days, the application view willInsertElement was sufficient for this purpose, but since views are passé, what's the accepted way to do this without them?

I thought about using willTransition on the application route, but that'll fire on every transition, not just the first time the application is instantiated.