I don't think you can currently place both a camera unit and an eye scanning unit on the same apparatus. It'll be a long time before you see this implemented into iPhones and iPads.
But on the subject of biometrics in general, it's increasingly clear that a big part of iWatch's appeal will be based on very ambitious medical breakthroughs that cover a wide array of health and fitness based use-cases. Whether it's glucose monitoring, sleep monitoring, heart monitoring, and even common health dangers for the elderly, such as falling down and being able to notify the iPhone to call for help.
Clearly the deployment of iBeacons is with iWatch in mind too, and I'm sure Apple and many others have all sorts of creative ways to make local commerce a more exciting and modern experience. Whether it's finding your car in a large parking lot, finding luggage at the airport, or all sorts of shopping and point of sale scenarios...
The iWatch in theory is an incredibly ambitious project, and I think equally important to its success are the user-interfacing elements. I think Apple will have some continuity with watches of yore by having the UI be largely passive, meaning you don't do a lot of interacting with it. Most of the features I described is glanceable data. Like a Google Now, it'll provide you with information when and where you want/need it. And of course, I'm sure Jony Ive partnered with guys like Paul Deneve is going to make for some amazing designs.
This thing will sell to every hypochondriac on earth. Not to mention the elderly, the health conscious, and many people with applicable diseases, etc,. These stupid smartwatches out there now that think they're solving a problem because they give folks the convenience of not taking their phone out to view a text are DOA. Apple is going to reshape yet another market, and I believe this market is one that is most uniquely suited to Apple's assets.