The "Apple Critical Alerts" API is clearly intended as a replacement channel for cellular emergency alerts[0]. (If not a "replacement", then perhaps a "supplemental" option. Redundancy is good when we're talking about whether "911" works).
The "Apple Critical Alert" API policy, restricting who's allowed to call the API, is a good thing. You just do not get performant public notifications if you allow just anybody to broadcast. (Milli)seconds count, people.
I hate Singleton patterns as much as anybody. And I hate when business happens behind closed doors, with limited public access, and restricted opportunity for public comment.
But again, if we're talking about the choice between """ locking down this one special channel, because it's responsible for real-time public safety alerts """ vs. """ asking how many broadcasters can possibly share that channel, before contention and congestion result in human-perceptible delays to alert delivery. """ Then I would opt for the former.
--- [0] You know how your phone will buzz REAL loud if there's like, an Amber Alert or Tsunami or something? That's a feature of the cellular system. To my knowledge, emergency alerts and 911 calls go over a separate dedicated mini-channel, which has gone by various names through POTS/2G/3G/5G and beyond. A.K.A.s: - Public Warning System (PWS) - Wireless Emergency Alerts (WEAs) - CMAS (Commercial Mobile Alert Service)