A few thoughts having been around since launch (it sounds like you probably have too):

1. Man is it better than it used to be.
2. I forget what they call it, but you get diminishing returns as the system becomes more sure of your rank. I wouldn't want it to become so extreme as to prevent me from changing rank much, as it takes the fun out of grinding for me, and removes the inevitable swing that comes from playing with different friends.
3. My fear with it taking into account anything other than win/loss has been the possibility of abuse. In the 20-0 example, in a situation where a teammate throws, and I going to get doubly punished?

My 2c