Sure, but unlike heart conditions where people often have no idea (about afib, or even abnormally high or low heart rates), people generally know when they have respiratory difficulties. Like the other comment noted something about family having pneumonia, and I cannot understand how the watch would have made their situation better. If someone in that state wasn't already seeking medical advice, it's hugely unlikely a watch saying "yo it's bad bro" is going to help.
It's like heralding a G-sensor in your watch telling you that you're falling. It's likely pretty obvious already.
Seems to me, it has some value (again, if it's accurate) for letting people know about sleep apnea; especially as part of an overall sleep tracking dodad.
I've got enough mild asthma around me that we have a finger pulseox (or two cause we "lost" one and found it later) and I've started yelling at sick people to check it once in a while. Cause they don't usually think to, but sometimes it lingers and by the time they decide to go into an office, the numbers are pretty low.
Of course, we're not on the Apple bandwagon and stopped wearing watches once we got used to having pocket watches again.
It's like heralding a G-sensor in your watch telling you that you're falling. It's likely pretty obvious already.