This should have probably been done for the 3.1.2 release. So I give it high priority as it should definitely done before the next release.
We are starting to get reports by users that files fail to decrypt with Gpg4win 3.1.2 and they only see the generic "Decryption Failed" error. (e.g. https://wald.intevation.org/forum/message.php?msg_id=6037 )
I think the problem is in GPGME actually. (Also see T3714 ) As the decryption result should provide the correct error. But we might also use the new flag for legacy no mdc to improve the handling in Kleopatra.