It’s not reserved only for certain people. As code owners, we make a judgment call based on an informal assessment of the feature’s prospects and how much work it would take to maintain it as a branch for a few months. Sometimes the Language Working Group gets asked for their opinion on the first point.
If the feature is merged but doesn’t seem to be making progress, it may be removed. For what it’s worth, that has happened to work by Apple engineers.
Again, this is all development process, not evolution process. Is there a reason you’re interested in this?