There would have to be some serious improvements to Apple Watch for me to buy a new one. Whlie body temperature would be welcomed, it’s not a must have game-changing feature. At best I struggle to to justify having my series 5 when mostly I use it to tell the time and maybe unlock my phone when I have a mask on.
If they came out with a round Apple Watch I would probably consider upgrading as I’ve always been partial to round smart watches. I’ve never liked the look of the square blocky aesthetically displeasing current design. However, I think this is very much a subjective thing.
As for a game-changing feature, if the Apple Watch came out with a model that could virtually replace the iPhone, esp. while going for jogs, or similar work outs that would be cool. Imagine not having to carry a phone and you could just use your watch? However, too many people need the large screen and let’s face it, Apple wont build a device that can hurt sales of another device. Apple wants you to buy a device for every scenario.