I would like it to be thinner, which is a little funny considering most Apple products are on the edge of being to thin. But the watch would look much nicer if it was thinner.
As for being circular. I am going to say HECK no. I really think a circular screen on a smart watch is just freaking stupid and backwards. There is a reason why watches were circular and why the watch face is circular, but that does not apply now that we have moved away from mechanical watches.
Why would we be hindered by that when there is no reason for it? A circular screen is just awful for display information, it's not good for anything other than telling the time. So I really hope this never happens.
Other thing I want to see the watch get is a 4G connection. I'd love to see a future where maybe the watch can replace the phone for certain people. Pair it with AirPods and you got all the phone functionality. Then you could use it with other devices like the Mac, iPad, or a new iPod Touch. When you are on any of those devices the watch pushes the phone functionality on to them. Would be an interesting place to arrive at with this technology.
But battery life needs to really improve. The Serie 2 is pretty good, I even wear mine when I sleep. Only charging when I shower in the morning and eat breakfast. However if you add an always on cel connection to it that will change quickly.