There would need to be three things that none of these smart watches have.
Durability. At the least, Timex or Casio G-Shock level. I want something I don't need to worry about getting wet, getting knocked, or getting dropped.
Duration. They can never get it to a watch's timeframe, but at the least, get it up past a week of use without a recharge.
Media use/bluetooth. Make it so it can take a micro-SD card, and play media to bluetooth headphones. Also, if you want that online experience, make it so you can act as a relay on your person between the phone and your bluetooth.
With tech today, I wouldn't want one. I think the time you can miniaturize it to give features such as call reception, streaming music, etc, will be the time it will be functional enough to sell. Otherwise, am I too lazy or distracted in my life to not hear/feel the phone, or to pull it out of my pocket? I have a phone for all that stuff, and a watch for time, both of which do that well. I don't need something that tries to help do both half-assed
For large values of one, one equals two, for small values of two.