Powdered snow is interesting but what is more interesting is freezing. I've always wanted a freezing mechanic in Minecraft and this hopefully just the beginning for this effect. It's also not a potion effect which is even better. I'm sure they'll give other mobs proper immunities such as polar bears and snow golems.
In the Q&A video they stated that the Nether will get no updates in 1.17 since it just got updated (even though it got ravines in 1.13; an update about water).