It would be all the assets in the default asset manager in the engine (so readily available). The assets for the editors will be loaded in a separate asset manager so they will not appear in the editor. This is actually happening already in the dev branch.
Also, the idea of loading a project was one that I struggled with for a long time. I finally settled on having the editors as more of an add-on for the game (which would not be added for the release of course) similar to the way the console is. Or another way of thinking of it is that we are just taking the console and extending it. It's a little bit of a paradigm shift from the old TGB but it saves a lot of effort that we don't have the man-power for. So the game loads as normal and somewhere in main it loads the editors which do everything they can to stay out of the global namespace and base asset manager. Of course, the editor is loaded as modules and if the game had modules with the same name that would be a problem. With that exception it should work great. I currently treat the Sandbox like the "game".
Also, I've set up a library fold that I want to have reusable modules in. I hope to create a "Module Manager" that can add modules from the library into your game folder. There's already code to copy modules so this actually might be easier than it sounds. In the future I hope to have a lot default functionality built as modules so that people can quickly prototype ideas. For example, a dialog box module for an RPG type game. I image after copying it the user will need to make changes but it will give them a quick starting point. For now the library just has the AppCore module in there.