Personally the perfect smart watch for apple devices would be/have:
-An e-paper display so it would be easily visible in many outdoor situations and have good battery life
-Siri enabled. I know some people think its crazy to talk into a watch but it would be very helpful. Set reminders, send texts/emails, etc. all without even touching your phone. It would also have a speaker so you could hear incoming messages (great for driving)
-Vibration function for alerts/notifications