Arduino decided today that libraries with a name value in their library.properties file starting with the word "Arduino" will no longer be permitted addition in the Library Manager index. The reason is that Arduino wants to reserve these names for their own official libraries.
Note that this restriction only applies to the name value in library.properties. It does not apply to the repository name or the header file name. However, it is best practices to make all of those match as closely as possible, since the Arduino IDE uses this as one of the determining factors in which library gets priority when multiple libraries contain a file that matches an #include directive.
Note that libraries with a name that is not compliant with the new policy will still work fine when installed via the Arduino IDE's Sketch > Manage Libraries > Add .ZIP Library, the Arduino Web Editor's Import feature, or manually installed. This is only about the Library Manager index.
There is no indication of plans to apply the policy to libraries which have already been added to the Library Manager index.
Since a name change is much more disruptive once a project has been well established, I recommend that everyone use library names compliant with the new policy in their new libraries, even if you don't have immediate plans to request addition to the Arduino Library Manager index.
Library Manager offers the easiest way for users to install libraries, get notifications of updates, install updates, even roll back to previous versions. I urge all library authors who have not done so already to consider adding their libraries to the Library Manager index.
Information on adding your library to the Arduino Library Manager index:
Information on the library.properties metadata file: