Apple Watch doesn't see many significant updates year-over-year on hardware or software. The mature platform has little wiggle room, but ever-improving chips and algorithms could introduce new features in watchOS 12.
In recent years, Apple has relied on existing data to generate more actionable information for users. Whether that's sleep apnea alerts, the Vitals app, or trend analysis on Health data — it's taking what already exists and making it more useful.
Apple generally introduces a new watch face or two each year, so expect some new ones that take advantage of the ever-expanding Apple Watch displays. There's still very little chance of a third-party watch faces store coming to the platform.
Rumors suggest Apple is planning an ecosystem-wide redesign that will bring the other operating systems closer to visionOS in design. Such changes could come to watchOS 12, but likely in limited ways.
Apple will reveal watchOS 12 during WWDC 2025 on June 9.