As a player who likes to mess around a lot, t-bag some foes, teamkilling my bros. I really don't want everything I do to determine my rank, because that would be wrong. I want the social playlists to screw around without the stress of my EXP on the line. I also think for many people getting a 15+ K/D seems nearly impossible. I would lower that to 10 or even 5, because being even +1 means you applied benefit to your team, unlike those who DID go negative, who made your team lose.
Also it seems from screenshots and gameplay the game isn't completely determined on kills. It has a point system which goes off of not only the amount of kills, but the type of kills. So this system you have created would have to be altered, or at least adjusted for these playlists.