Here's a thought: Suppose you are stranded in a national park in say, January 2025 (after the free subscription is no longer offered) and you suddenly realize you are not paying and don't have access to call for help. I would imagine that you can use your phone to subscribe right then and there (as the hardware is built into the phone).
What's to stop someone from simply signing up in that emergency scenario, receiving emergency help, and then cancelling the paid subscription immediately afterward?
My point is that SOS doesn't really make sense as a paid feature. I think Apple should just offer this for free as part of iCloud (or at the very least, included in iCloud+). Free for everyone, and another example of a premium feature that is built into the Apple ecosystem.