"I'm concerned it will be quite annoying for Fedora-only devs, though"
Fedora does not pick patches from RHEL since RHEL kernel is much older usually and Fedora is following the latest upstream. When RHEL is used in Fedora infrastructure, there is no kernel patching involved.
"Overall I have the feeling this will mostly inconvenience legitimate uses of the RHEL kernel source"
Legitimate users as in customers have access to a source browser.