I hope you'll be able to upgrade the module and retain the same case+band, but I haven't seen anything definitive from Apple to say that's likely.

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.

Hmm, I doubt it would be ultra-slow. They'll probably bring out new ones somewhat regularly (maybe every second year).

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

Sure, but I think this is more of a concern for the non-aluminum models, where the case is substantially more expensive.

Have you ever heard of an apple product where this was the case?

Mac 128k to Macintosh Plus was a motherboard (+ backside) upgrade.

My money is on some kind of trade-in/up program.

I wouldn't be shocked if they did nothing though.