According to Shigefumi Hino, the action where a blue Pikmin can rescue a drowning Pikmin was added by Yuji Kando without the knowledge of the developers. The programmers added lots of gestures to the Pikmin on their own.
I've always felt this mechanic should return. It's really niche and hard to get value out of but I did find myself using it quite a bit in Pikmin 1-2 and found myself missing in 3-4.
I didn't even know this feature existed until Pikmin 4 came out. That's how relevant it's been. I don't even remember if any Let's Players that I watched used it to show it off in the first two games.