"If" Apple is working on health monitoring, and I genuinely think that they are, I believe this will the firing pistol that starts the arms race that leads to kind of increases in human life expectancy that the theory of accelerated returns predicts.
Unless there's some major improvement in data sources (i.e. sensors) it's very difficult to see what Apple are going to achieve here. They've managed to surprise people before, but breakthrough medical sensors (especially around blood monitoring) would make previous revolutions look minor.