RACF has an upgrade action for z/OS V2R4 which states:
Ensure that the ECC master key is activated in the CCA coprocessor
Is this something that is valid for ACF2 in z/OS V2R4 as well?
Yes, this is valid for ACF2 in z/OS V2R4 as well if ICSF is being used. It applies to usage of the ACF2 GENCERT command with ICSF related keywords in z/OS V2R4.
See CAS20E0E ICSF CSNDPKG service error during ACF2 GENCERT for information pertaining to the error that occurs by failing to provide an ECC master key.