Apple
Reliable analyst Ming-Chi Kuo from KGI Securities says you shouldn't expect the next Apple Watch to look any different from the first-generation model.
According to Kuo's most recent research note, which was obtained by Apple Insider, the Apple Watch 2 will include "spec improvements with limited changes to form factor design."
In other words, it looks like Apple Watch upgrades will closely mirror how Apple handles each new iPhone: Every two years or so, there will be a new device with a completely new design, and in those in-between years there will be new "S" models with spec upgrades but no new exterior design (or minimal changes at best).
As far as the actual changes in the Apple Watch 2, Kuo didn't offer any details about the device's internal parts, but 9to5Mac's Mark Gurman offered some possible insight in a report from last June. In that report, Gurman said Apple will add a FaceTime camera to the Apple Watch so people can make video calls from their wrists, and he also suggested it will have better battery life, more independence from the iPhone, and more variations between the $1,000 and $10,000 price points, in an effort to keep pushing the Apple Watch towards the luxury crowd.
Kuo doesn't offer a launch window for the Apple Watch 2, and neither does Gurman. Apple unveiled the first Apple Watch two years ago this September, so we could see Apple unveiling the second-generation model at this year's September event, where it will likely also unveil the next iPhone. However, if the Apple Watch is only getting internal upgrades with no changes to the form factor, we might see a new model even sooner than September - after all, Apple did just drop the price of the first-generation Apple Watch by $50 last month.
Apple's next event (that we know about) will be its Worldwide Developers Conference (WWDC) in June. Perhaps we'll see Apple unveil a new Watch model there to coincide with some new software upgrades for Apple's mobile lineup.