It'll be too bad if they decide to charge for this ultimately. This feels like the kind of thing that should just be factored into the cost of the device and its expected lifetime.
Unless you're the type of person who is regularly venturing out into remote areas, I doubt most people will want to pay for something that is very easily perceived as "never gonna need that". While it's a new flashy feature, people might, but it's going to be free for 2 years, by which time it'll be "old news". And if in those 2 years you never needed it, the odds that you'll decide to pay for it are even lower.
Except you never know when you might suddenly need it. You might spend 99% of the time in the big city, but once a year or even less often you head out on a road trip, passing through some areas with no coverage. You might not even think of it at the time. And suddenly you have a breakdown and that's when you really need the service... and you didn't think to subscribe to it since it didn't even cross your mind. Are you now doomed?
There could be some VERY bad PR from that. "Man dies in ditch, couldn't send for help despite having new iPhone 17 because he didn't pay for sat emergency service before leaving home."