The old ranking system was done by election, with the associated risk of higher-profile teams being ranked highly simply based on their status. Now, teams will be ranked based on an average of ranking scores for each bout, which each include the importance of the bout, the difficulty of the opponent, and the bout score itself.
Tournament bouts count more than regular season bouts, and the championship is the highest value bout of them all.
The old system ran the risk of voters considering non-sanctioned play; the new system requires that all bouts be in a sanctioned situation to count for a team's ranking.
As well, the WFTDA are adding a division structure to their system. The top 40 leagues are called Division I, and required to play at least 3 bouts against other D-I leagues.
Once per year, the divisions will be reset according to overall rankings. If 4 D-II teams now find themselves ranked in the top 40, they will promote to D-I consideration. It's even possible for a D-III team to go straight up to the top flight!
Two difficulties are the system for catching inaccuracies, which apparently requires a majority vote of all the leagues to call for a recalculation, and the fact that teams may change divisions in the middle of a tournament season, which runs from July to June.
That said, it's great to see one of the most powerful organizations in the global game moving toward using a fixed structure and quantitative data to rank teams. I look forward to a more competitive and more interesting 2013 WFTDA season.