Sounds more like a github request than a forum request.
The source code found in src folder and all its subfolders is compiled and linked in the user's sketch. Only the src folder is added to the include search path (both when compiling the sketch and the library).
For backward compatibility with Arduino 1.0.x, the library author may opt to place source code into the root folder, instead of the folder called src. In this case the 1.0 library format is applied and the source code is searched from the library root folder and the utility folder
The content of the extras folder is totally ignored by the IDE