Watch faces don't have access to communications services, so getting actual live weather data is going to be impossible.
Watch faces don't have access to position data, so getting the sunrise/sunset times.
The color palette supported by devices is not as good as what you're seeing in that simulated image. On the 920 (and possibly other devices), there are 14 predefined colors. So displaying fancy ghosted numbers would not turn out as pretty as you're seeing.
That rendered screen has super high resolution. The current crop of Garmin devices are limited to 205x148 or 218x218 which is about 2/3 of what you'd see from a smart watch type device like you're looking at.
