If it is possible to have multiple revisions of libraries you will have multiple revisions of libraries. I've seen this play out "at scale" and what happens in

If it is possible to have multiple revisions of libraries you will have multiple revisions of libraries. I've seen this play out "at scale" and what happens in practice is software rots until some kind of crisis or feature demands an upgrade. At which point somebody creates another set of branches to solve precisely their problem and nothing else. Maybe it's just where I've worked, but atomic commit carries with it some strong cultural norms that make it really tractable to have one version of everything. If code compiles and automated tests pass, the change is safe and may be committed unilaterally. Inevitably things go wrong, but the post mortems for incidents don't lead back to the lack of permission from the affected projects. I wouldn't maintain software that can kill people in this way, but for everything else it strikes a nice balance.