If Apple continue this approach through to release, there will be far more complaints about the inconsistent mess it currently is than there ever would be if Apple took this truly system-wide.
We need to remember that this is a user selectable feature.
Those that have been looking forward to Dark Mode since iOS 7, like me, have always wanted it mandated across as many aspects of the UI as possible.
For those that aren’t bothered about it, the future will remain “bright” as the default of course is Dark Mode set to off.