There's nothing in the actual datamined data overtly pointing to Spiritborn being a nature-based class. The entries just mention wings and flight animations with a single line referencing armor thorns. Angels have wings. Valkyries have wings. There are very few mentions of Spiritborn in the data that was shown in the video as well, and it could easily be a placeholder name.
Spiritborn does not sound like a Diablo class name at all:
- Barbarian
- Druid
- Necromancer
- Rogue
- Sorcerer
- Spiritborn?
The name itself does not invoke strong themes or an easily identifiable fantasy archetype. Druid also already exists. They are not going to have 2 nature-themed classes in a game with 6 classes. There's a reason D3 never implemented a Druid class. Witch Doctor already filled that design space, among other reasons of course.