It never became a sellable feature of the calculator. Why? It was never accurate enough. It's clock was off as much as an hour a day. It may very well be that the Apple version may have the same problem with its oximeter.
You gotta keep in mind two things here. One is that Apple is moving into the Health market in a big way. The second thing is that the FDA is going to be involved in the approval process.
Those two things tell me ... “It’s coming!”