A slight problem with your amazing Ideas...
Problem 1: Yes, I understand these ideas are absolutly incredible, and they are to die for. Well, maybe not to THAT extent but its pretty good. Where would we even GET these models? Also, the coding would be very difficult. I suppose we could have a system where each type of prey has different amounts of HP, and like IT and IW, we can attack and destroy the prey, but when your crouching, they cannot detect you. This might be a reason also to add shadows. When you kill something, no matter what it is in this game, you can eat it. Each prey has different amounts of meat. One meat is one bite.
Problem 2: Finding the people to code/mesh. Meshes can be easily animated and created through a program on blender, and there should be a tutorial on the FH site somewhere, under member tutorials.
Well, thats about it. Prey doesnt cause lag, don't worry, I have seen many games...