Wearables are not all smartwatches.
Wearables are, currently, not very good at input. Not just me, but anyone who writes about their serious love of anything (mostly smartwatches) says the game changer is near-ambient notifications.
Also: gathering general info, such as fitness trackers. But that's sensor extension, not deliberate user input.
Future tech is full of wearables http://www.technovelgy.com/ct/SrchRes.asp and there are already (mostly experimental or very, very specialized) smart clothes.
Open Questions
I would love to research these. I have ideas how, but have yet to get anyone to help me.
- How often they are glanced at.
- How quickly (and frequently... success rate) after a notice they are glanced at.
- How often that results in further actions.
- How often used for ambient info. Time, weather, etc. that is always displayed.
- Issues with not-always-on devices like Apple Watch.
References
* https://developer.apple.com/watch/human-interface-guidelines/