Safetynet was not a mistake; it was a lock-in mechanism. Widespread failure to call it out as such and oppose it as happened when Microsoft proposed something similar for PCs a decade earlier[0] was the mistake.
> will this mean we have to support one more standard, one more release channel, one more modified OS?
Android apps don't have to take any active steps to support third-party distributions. All they have to do is refrain from taking active stops to block them, but I suspect you knew that.
[0] https://www.nytimes.com/2003/06/30/business/technology-a-saf...