Probably nothing. Most people upgrade their watch because the one they are using is too old, damaged, or wants a new watch every 2 years. The issue is that watch is a well developed product where the updates every year is very small and it is viewed as a "crash grab" more than an actual upgrade. Yes true the display is "better" and you get 5G service on the U3, it doesn't give the user an "urge" to upgrade.