If an algo is given for --quick-gen-key only the primary key is created. We could extend extend the ALGO specification to allow for example "ed25519/cert,sign,v5+cv25519/v5" for that parameter and create a subkey with the specified algorithm (here using the v5 key format).

A further enhancement would be to allow the creation of more than one subkey. However, this requires major refactoring of keygen.c.