It's not a secret! I got an email a few weeks ago with some requests that I liked, including harpoons a la cone snails. Motion-eyes is an interesting idea... my science-brain says to make it be the relative motion between it and the prey, but that might end up being really hard to use. It's always hard to strike a balance between simulation-accuracy and gameplay usability.
Setting up the tools to be able to make a predator-prey ecosystem is my ultimate goal as well. Someday. There's a lot of work to do in the engine beyond just adding new body parts.
I should probably convert the comment section on the game page to a forum to make it clearer for where to put suggestions/bugs, but I've been putting it off because it clears all the comments.