Important details further down: https://grapheneos.social/@GrapheneOS/117282129725629495
So it seems like the problem isn't that the new API is Pixel exclusive, but that the first and third quarterly release patches each year are Pixel exclusive?
QPR1 and QPR3 are now Pixel exclusive since Android 16. That means the new APIs for app developers added in Android 17 QPR1 are Pixel exclusive until Android 17 QPR2. There hasn't been a case of new APIs for apps not being open source or not being available to every OEM since Android Honeycomb (3.x).