Library needs to really be useful.
I think what I would expect a library to have would be:
Lower thirds that were created using the graphic panel (saved transitions used to introduce those lower thirds)
A color pallet
Perhaps an opener and closing slate. These simply could be the graphic elements saved in their proper sequence before rendering to a video.
Typically in the past I would have to search for an old project, open it, copy those elements to the now project, then find the actual assets such as music, fonts (if using a different computer) logos ect. and copy those from the previus project to the new project. Again it would be a huge improvement to have all of this accessible within a library. Even if the library was linked to my own personal dropbox or cloud account.