Do we observe general intelligence in nature though, here on Earth implemented with the materials available in our environment? If so, it’s a bold claim to make that it will always be impossible to achieve it artificially.
The same is true of AGI. Of course it's possible. but right now no one has any clear idea how to do it without extreme brute force.
Personally, I think it's more likely that we'll have a working Alcubierre drive before anything approaching general intelligence
Impossible due to physics limits. Human lungs have 57 square meters for extracting oxygen from fluid with 21% volume oxygen. 30°C air-saturated water have 0.5% of oxygen, so working gills for human would need surface area of 2394 square meters.
You’re making the same mistake as those who critiqued the concept of heavier than air flying machines, starting from the assumption they must work by flapping their wings. As it happens now we have wing flapping drones anyway though.
“Ever” is a very, very, very long time.