Just as a reference to what can “break” with Stream being not the target: Foreman 3.1/Katello 4.3: pulpcore has newer version of createrepo_c-libs on CentOS 8 stream - #3 by mhjacks
But of course it would also be the other way round if this would be the target and the newer version would be required but has not landed in RHEL and Rebuilds.
And I would still argue that it is better to not break upstream and downstream has to wait than probably not recognize that something would be broken on upstream and than still getting hit on downstream.