Images should be able to use any drawable

[karai17]

An Image element should probably be able to use quads so that a user can create their own image atlases for icons and whatever else.

[adrix89]

You are probably better off with resource management system that can be set up independently. You can set defaults for types automatically. Note that if resource management does not have some serious automation it will be a pain in the ass to setup manually. Its one of the greatest reason why I am going with a visual editor for my GUI.