Nexus Watch UI Concept-UPDATE
This is my concept of what the Nexus smart-watch should be. Starting with the main screen, there is an analog clock , a digital clock, and the current temperature. If one then swipes to the left, then the app list appears. Once in the app list, rather than swiping left or right like in android 4.+, one scrolls up and down to reveal all the apps.
Since apps are restricted by the small screen size of the watch, which I would put around 1.5" x 1" or 2.0" 1.5" they must be simplified. One app that I personally think would be nice on the smart-watch is Google Hangouts.
I find video-chatting on a phone or tablet quite awkward. Between positioning the camera and holding up the phone, it just doesn't feel natural, which is why I think video-chatting with a smart-watch would be much better. Like holding it up to see the time, lifting your wrist seems much more familiar than holding your hand to your face. It also doesn't look half as weird.
Google Now is also a feature I think should be in the watch. It would be accessed by swiping to the right from the home screen. Needless to say, a full keyboard and a full web-browser are two important components of Google Now, and are two components that don't quite fit on a smart-watch.
First, Google Now would have to be searched by voice only. This could be a problem since voice search still has its issues, but with a good word correction list, the feature is still a plus. Next, rather than having a full web-browser, the search would just bring up information from the knowledge-graph. In other words, it would be much more Siri-like search than Google search.
Finally, comes the the task manager. Because of the screen size, only one app can be shown at a time, but scrolling up and down reveals the other apps open.
This is my concept for how an android-based nexus watch should work. If you have any Ideas or critiques, please let me know.
Edit: I've read over the comments and it seems like the general consensus is that the on-screen buttons have to go, so I've created the concept below.
When the watch is unlocked, this card above is shown. The time on this card could be changed from digital to analog and the card itself can be changed from a light theme to a dark theme.
Below is how the UI would be navigated; please note that the small display on the watch can show only one card at a time. If one scrolls up then the Google Search bar area of Google Now is shown. If one scrolls down from the main screen, then he comes to the apps card. The weather and calculator apps are examples of how switching from app to app would work. When an app is opened, it opens to the side of the apps card. In order to get to get back to the apps draw from the open weather app, one must swipe to the right. In order to go to the calculator from the weather app, swipe to the right. Also, open apps can be closed by swiping up or down.
Below the apps card are cards that would not be considered apps, such as a notification card or a settings card.
This is the updated concept, and again if there an any suggestions please let me know. Also, a few people mentioned that I'm cramming a phone into a watch, which gave me an idea. Why not answer your calls from your smart-watch through a Bluetooth headset? You know, innovation.