There can be a single floating "add" button, and when you click on it you can choose if you want to add a scene/external events/external layout!
It is sounds interesting, definitely worth a try and see if it works all places
Resources manager won't be deleted, but the goal is that new user should not need it
And how do you plan to make the current method and the resource manager work side by side? Because at the moment if you click on the add new animation frame it opens the file browser and when I click the resource manager it doesn't really do anything at least for now.
I think it would be nice when we click the add new animation frame button it would give us the option to open image from resource manager or load new image from local drive directly.
I understand where you want to go with this, but in huge projects with thousands of potential images, in my opinion all user get to the point when they want to and have to organize their images. The question is where should be the place to organize them. The file system, so the people must organize their images in to folders inside the project folder or it needs to be the resource manager so people don't need to worry about how the images are stored locally inside the project folder.
I think it need to be the resource manager especially if you want to allow people (new user) to open images from anywhere even outside the project folder and GD need to deal with it locally. So you either force even new users to mess around the file system to organize their images or let them organize their images directly in GD so they don't even need to bother with the project folder. I think the latter is more (new) user friendly.