[AnthonyMouse]

My impression was that you were talking about API changes that actually require the developer to use them, e.g. because the old thing doesn't work with the new system anymore. Then you give them some notice and they're ready with the new thing because they want their app to keep working.

The things you're listing are optional features. That doesn't require some kind of coordinated effort. If one distributor requires support for Dark Mode on day one and another gives developers a year and another never requires it at all, so what? If you really love Dark Mode you can decline to install apps from distributors who don't require it. Or just decline to install apps that don't have it, which you could do regardless of what any distributors allow.