What if there were 2 prestige systems? 1 for PvE and 1 for PvP? The PvP one would be similar to how CoD does ranks where each win gets you exp. pts. You could also have a combined prestige where the two systems are balanced (because of people doing a lot of PvP and therefore earning a lot of prestige) and added together.
Err... the rank works somewhat like that.
And remeber it now gets reset every week because newer people would never catch up with those that were already playing before so we didnt like it.