In a Gerrit conversation, Catrope noted:
One minor thing we may or may not care about: the entry for the "r" in the RC legend doesn't go away when you set $wgOresUiEnabled = false; . It's added through a config var directly in extension.json, so if we wanted to fix this we'd have to add an init callback and conditionally set it there. I considered doing that for other reasons (user may have prefs set such that "r" will never appear) but not sure if it's worth the effort.
@Catrope: It doesn't seem like we can rely on having BetaFeatures loaded at extension.json callback time? If not, then fixing might cause the "r" to become unstable for beta-enabled users.
This task is complete when we have discussed and found a way to hide the legend when not in use.