[s_tec]

I feel like this is an obvious idea, but we simply haven't had the 3D printing technology to make things like this before. Casting this using traditional methods would be extremely difficult. Nobody bothered making stuff like this, not because they never thought of it, but because it was always too expensive.

[Taniwha]

It's essentially how any mammal cools itself - so yeah, pretty obvious

[elil17]

The header is not actually meant for cooling, just to distribute the fluid evenly across the heat exchanger. 3D printed heat exchangers use shapes like gyroids.