It is possible although you would have to develop the framework to handle that yourself. It be worth looking at the engine source directly on GitHub to see how everything is loaded and handled currently.
All the assets including the scenes can be loaded at runtime and don’t have to be package as part of the ‘app’. The files can be hosted on a server somewhere as long as the URL links between assets are correct.
See here for an example for loading a 3D model at runtime: Load 3D models at run time from a PlayCanvas application
The only exception to this would be the scripts that you create. I can’t remember offhand how the scripts are reference by the entity in the scene JSON files.