If projects do not hide their releases, it can be easy to
accidentally upgrade one component without updating another
Ok, got it. However, I'm still convinced that a "hiding" policy is not a viable solution for this problem. The solution is proper OSGi version numbering, which scales independently of how p2 repositories are deployed.
And since many people don't update to SimRel on the day of the release, this transient state of older SimRel version with newer components visible is affecting all those users already, even with a "hide" strategy.
So hiding isn't a sustainable solution for this issue IMO, so that it'd better being dropped from the requirement/process to make things simpler for everyone and drive projects to find real solutions if they suffer from such versioning issues.