I think the legality of a emergency drone can be overcome, so I'd not worry too much about that, but the weight and distance it can travel may be a hurdle that's difficult to overcome right now, but that could change with technology advances soon enough.

But, as mentioned here, a drone that goes looking for someone who's lost or needs help is an approach that may have more potential as it could find and deliver aid before rescuers arrive and confirm the hikers location.

Finding a hiker might be approached by searching for signals from a phone or other devices that send a signal, like a "SPOT".

Another approach is maybe using a drone as a relay to send a message or phone call. Here in the Ozarks, for example, it's easy to be down low in a creek between hills and not get a cell phone signal, but if you climb a few hundred feet up you can get one.

This idea has merit.