There are many reasons why some libraries are not open source, such as security- or quality-related considerations. For the specific fixes you have in mind, you are encouraged to use
Public Issue Tracker to submit your requests in form of issues or feature requests. All of these will get assessed for merit, and addressed in accordance, eventually implemented. The "Google App Engine Community"
page documents various ways in which you may get involved and contribute to App Engine Platform development. You should not hesitate to put your ideas forward, but follow the appropriate channels to make them known and implemented.