As far as I can tell, it's going to be similar to Debian Testing, ie. a rolling-release distribution that will have security support. RHEL point releases will then be snapshots of that rolling release with their own security fixes.

I can see the use for such a distribution (run CI against CentOS stream to catch any potential breakage with upcoming RHEL changes) but I think the way they went about making this change is ... unfortunate.

EDIT:

To expand a bit, things may still turn out positive overall if Rocky Linux succeeds and Red Hat doesn't pull off any other silliness. There's an opportunity here for Red Hat to really open up RHEL development to interested parties via CentOS Stream, and so long as they maintain their commitment to publishing RHEL as free software and don't actively interfere with people building their own RHEL-compatible clones from the point releases, everyone wins in the end.