Not to be pedantic but that's not how the history went. First there was PGP (the product), then that was turned into a standard (RFC2440, "OpenPGP Message Format"), and GnuPG implemented that.
Then, some (backwards-compatible) changes to the OpenPGP standard were proposed, and every implementation implemented them. (These were specified in RFC4880.)
Then, some (backwards-compatible) changes to the OpenPGP standard were proposed, and many implementations implemented them. (They never ended up in an RFC, but are now dubbed "LibrePGP".)
Then, some more (again backwards-compatible) changes were proposed, and many implementations implemented them, but not GnuPG, for now. (This is the crypto refresh. It should become an RFC soon.)
It's a shame GnuPG doesn't want to implement the crypto refresh at this time, but that shouldn't cause incompatibilities (if all implementations are conservative in what they generate). Messages sent between GnuPG and other implementations can still use RFC4880 (the old OpenPGP standard), they just won't benefit from the improvements in the crypto refresh, unfortunately.
Then, some (backwards-compatible) changes to the OpenPGP standard were proposed, and every implementation implemented them. (These were specified in RFC4880.)
Then, some (backwards-compatible) changes to the OpenPGP standard were proposed, and many implementations implemented them. (They never ended up in an RFC, but are now dubbed "LibrePGP".)
Then, some more (again backwards-compatible) changes were proposed, and many implementations implemented them, but not GnuPG, for now. (This is the crypto refresh. It should become an RFC soon.)
It's a shame GnuPG doesn't want to implement the crypto refresh at this time, but that shouldn't cause incompatibilities (if all implementations are conservative in what they generate). Messages sent between GnuPG and other implementations can still use RFC4880 (the old OpenPGP standard), they just won't benefit from the improvements in the crypto refresh, unfortunately.