I couldn't find such requirements when reading the GPL.
The paragraph cited by GP is from the explicitly about "convey an object code work under this section in, or with, or specifically for use in, a User Product, and the conveying occurs as part of a transaction in which the right of possession and use of the User Product is transferred to the recipient in perpetuity or for a fixed term". So in other words, only if you sell hardware with binaries under GPL.
Also, from reading other comments, it seems it would still be possible to use the adb console to load apps without having signatures? So that should cover it as far as the GPL is concerned.
IANAL but isn't that the purpose of the passage below (emphasis mine)? I agree it's subject to interpretation whether the license also allows one to provide detailed instructions on how to obtain new keys from a third party and install the application using them. However, it seems to me the passage implies that if Google is to deny someone developer keys and installation of the modified application, then the original distributor of the application is in violation of the GPLv3.
----
'“Installation Information” for a User Product means any methods, procedures, authorization keys, or other information required to install and execute modified versions of a covered work in that User Product from a modified version of its Corresponding Source. The information must suffice to ensure that the continued functioning of the modified object code is in no case prevented or interfered with solely because modification has been made.
If you convey an object code work under this section in, or with, or specifically for use in, a User Product, and the conveying occurs as part of a transaction in which the right of possession and use of the User Product is transferred to the recipient in perpetuity or for a fixed term (regardless of how the transaction is characterized), the Corresponding Source conveyed under this section must be accompanied by the Installation Information.'
But the "original distributor of the application" is not convoying the binary in "a transaction in which the right of possession and use of the User Product is transferred to the recipient", so that clause doesn't apply.
In this context, the "User Product" would be the phone, as defined in the previous paragraph of the license.
The paragraph cited by GP is from the explicitly about "convey an object code work under this section in, or with, or specifically for use in, a User Product, and the conveying occurs as part of a transaction in which the right of possession and use of the User Product is transferred to the recipient in perpetuity or for a fixed term". So in other words, only if you sell hardware with binaries under GPL.
Also, from reading other comments, it seems it would still be possible to use the adb console to load apps without having signatures? So that should cover it as far as the GPL is concerned.