In the wearable PC labs and geek tech corners of the web are gloves, bracelets and ring mice. These all tend to look bulky and not something you would want to be seen wearing away from your desk, or even in public. However a recent Kickstarter project funded a device which shows promise.
I would not be surprised if Apple did not create a ring input device as an addition to other existing and future devices. It could work with Apple TV, your Mac, iPad or a future glasses project. With their design and engineering flair they could make it usable, discrete and fashionable.
I see a future where we will wear multiple connected wearable devices. Selecting the best of breed for each situation. Just as we can currently pick the mouse and display that fits our needs and budget.
Another entrant into this area. These are just concept designs form a competition on crowdSpring but even if this device does not eventually appear I have no doubt that rings will be important input and control devices. They are small, personal, unobtrusive and can be used without making large gestures.