While I don't know how large this group is, skiers, hikers, boaters, campers, off-roaders would all likely get use out of this functionality.
Hahahahahahaha! Not a chance. Maybe the over landing crowd, and hardcore hikers, but most casual enjoyers of the outdoors definitely do NOT have a Spot or InReach. Next time you’re on a ski hill, ask around - you’ll be shocked how few people have them.
and for a life saving device like this i know a subset of people will not want it a part of their phone.
...but this will definitely take a LOT of business from garmin because i believe that subset to be pretty small.
With that said, the iPhone (Pro?) is becoming somewhat of a swiss army knife for casual tramping: offline maps with GPS and a compass, an excellent set of cameras, an ereader, excellent battery life to back all that up _and_ it can now communicate with the rest of the world in non-life threatening -- but marginal -- situations. As an example, we leave intentions with people whenever we leave ("here is our route, if we're not back by midday on the third, contact SAR"); being able to message people and say "hey, I've rolled my ankle, we're safe but will be late because we're limping out, don't worry" is a pretty excellent feature.
We're probably a niche market, but several friends in that community are pretty excited about this feature. For 2-3 day trips, this makes the outdoors much more accessible.
Kind of like how Collision Detection could have been an excellent Apple Watch upsell feature but was brought to all iPhones anyway.
They recognize the power of things like fall and afib detection for pushing into the ever growing consumer Health market.
It's a great feature but it's far from a guaranteed money maker. This could just as likely disappear from future iPhone models.
edit: also competing dedicated devices also include the cost of SAR insurance in their monthly fees, which are significant: https://www.garmin.com/en-US/p/837461/pn/010-06000-SU
It starts at $15 a month but any serious user is paying more like $35-65 a month.