There is a plugin by VRAdultFun that animates the hands and makes them responsive to interaction and posing, giving them fluidity. However, there is no such thing for feet. I've searched for sometime, perhaps I've looked over something but I have not seen anything like it. I personally would really love to see something like that. Nothing crazy, just someting that gives some more life. Obviously modifiers for frequency of scrunching or flexing could be part of it, but it's not necessary.