based on the rumors from Mark Gurman and others, plus based on the Apple Watch history of keeping the same screen size / case shape for 3 years, it is very unlikely to see any body updates or new buttons until 2024 with the Series 10. the series 7/8/9 are "this" generation. I do think we finally see a major CPU update after 3 years of no real change and the Series 9 may use this new CPU to finally make some sizable battery life gains. since I also believe the Ultra will see a Series 2 this year with the same insides, perhaps its battery life also gets longer yet.
Sounds totally plausible.
As Apple typically adds at least one extra thing from generation to generation, I am really curious what this will be this time for the Ultra 2 aside from the CPU update.
5 to 6: SPO2 sensor
6 to 7: larger screen, faster charging
7 to 8: temperature sensor