The smartwatch market will grow, others will compete, and even though Apple busted open the market, it will be necessary for them to try and stay ahead of the pack.
So while I wouldn't necessarily expect something as rapid as iPhone updates, I doubt we will see more than 2 years between Watch iterations, maybe less.
Also, the Apple Watch 2 will have a 4K screen.
4k screen? On a watch? Bs and useless