The current state of player rank is based on a cumulative player score stat that is recorded by Steam. This is simply the Score you see at the end of a game added to the previous sum of all player scores you have received. This cumulative score is then compared to an array of threshold values to determine player rank. This is similar to an experience level system in an RPG.
This system was chosen because it is first, easy to implement and second, gives players a sense of accomplishment as they level up. More skilled players will level up faster. But a less skilled player could reach a higher rank just by playing A LOT. Therefore, comparing two ranks gives you a little information on the skill and experience levels of the players but nothing definite.
From BT: We're changing the goal of Rank away from using it as an evaluation of a team's chances of winning a match. Instead, we want to use it as a reward and a motivation to play. By granting rank on interval, and using the game economy as the reward driver, we're going to increase individual player investment in the game. The second job of Rank is to also discourage cheating. As a free game, we need player time investment to build up a sense of loss should that investment be sacrificed. By adding more levers to areas that we want to reward (probing, nanning), and adding bonus to points scored against high KB targets, or against higher ranking players we can really move the needle for players that are motivated by persistent points.
For those players who are not motivated by ranks and achievements, they're just going to stack it up anyway. It doesn't really matter how much we stack shame them.

This is all that is implemented, the following is future plans.
I want to add more opportunities to gain score to the game. Currently, it is mainly things like base kills and player kills. While these are fundamental to game play, it doesn't measure all ways to contribute to the game. Things like good probing and nanning are important but not previously recorded.
Additionally, many have expressed concern with "stacking" and how allegskill encouraged anti-stacking. To help offset this I plan to implement a factor on player scores of (opponentRank)/(yourRank). Therefore any score you earn playing on a team that is 2:1 stacked against is doubled and likewise halved on the stacker team. This should help drive the stacks toward unity.
I have been working towards these goals in my achievement work so I think I can do this in Two WeeksTM, err I mean two weeks.