Since Apple hasn't said anything about upgrades, I think that means that there won't be any. Apple will replace broken or faulty electronics, but they won't upgrade you to the newest model.

That really indicates that Apple Watch will evolve slowly. Maybe it will be three to five years before there's a new model. It doesn't really need upgrades, because it's mostly a fancy terminal for your iPhone, plus a fitness band and iPod shuffle. And I think that Apple will support it for a much longer time than iPhones and iPads. Ten years from now, today's Apple Watch will work with the latest iPhones and iOS.

But they will introduce new cases and bands every year.

The article explains that, at least for the aluminum watch, the "movement" (aka the electronics) are probably glued in.