Most of the new features of the Venu 4 are on the software-side, thus could be easily impemented on the Venu 3. But ofc, Garmin has no interest in doing so, they want to push the Venu 4 to the market and do not intent to cannibalise their own model.
However, as a customer and buyer of a Venu 3 (last February for 380€, mind you) I feel bad. I feel like Garmin cuts me intentionally out of the loop of new valuable health features, rendering my 10 month old smart-watch useless for future updates. I love the hardware, but this sucks, I am not amused. Garmin naturally doesn't care, but I am looking for a new brand, this is uncceptable and most likely my last Garmin.