ISTM that opinions vary on what constitutes a "release blocker", and maybe empowering only the release managers to make that call would be a good way forward--which is what ISTM is what the Dev Guide already says anyway. But I guess not!
I think that RMs are empowered to decide what is a “real" release blocker, but you need some mechanism to flag an issue as potentially a release blocker for the RM to make a decision on it. Making a decision on that potentially release blocker should also itself be a release blocker (because if it’s possibly a release blocker, then we should treat it as such until the person empowered to make that call has decided one way or another).
So I think for the system to work, you need to either allow anyone to flag an issue as a release blocker, and the RM is empowered to say “No this really isn’t” and unflag it, or you need two flags, for release blocker, and maybe release blocker, and both block the release.