Health monitoring stuff is in that category. It could become a thing in itself, especially if other sensors are added. eg blood sugar, not just for diabetics, but dieting, sport, concentration. general health.
Another huge problem with the self-quantification trend is there isn't much emphasis on doing stuff with that data. There's a fervor about knowing about yourself, but a large gap in utilizing that data.
Smart watches could very well fill that role. A nice first step would be to stop calling them smart watches. Wearables isn't much better.
Computers keep shrinking, from mainframes to desktops, laptops, smartphones. I'm curious about the next smaller form-factor, and argue it's not watches, but glasses. That was the claim I meant to make.