I live in rural NM, I have great coverage in town… but venture a little bit out of town in the wrong direction and you quickly lose service. That coupled with in the last year the single fiber line that feeds internet for my entire county has been cut 4 or 5 times, one of them being out for 4 days. This would be a welcome feature.
A -lot- of people use it for trail running and hiking, and Apple has been building out a lot of features for those users. Back tracking, trail maps, etc.
Messaging in dead zones would be a game changer for those users. Even in Apple’s home turf, the Bay Area, trail dead zones are very veeery common.
This feature would sell a lot of watches among the REI crowd.