I find that every now & then I want to change the data source of a layer in a map and realise I have not added a database (FGDB typically) or a folder to the project while browsing for the source.
Please add the ability to right click a folder or fgdb in the file browser window and add it to the project.
For me these are typically additional folders or databases such as updated government reference data, temporary processing folders, etc. that I may use a few times and it will be faster to have them in the Project section of the file browser.
This doesn't replace any of the other methods of adding stuff to a project; just makes this one incidental discovery of need a bit easier to digest and more efficient.