From what I have read (previous 538 blog post on Messi), they are already tracking a good deal of data about the games. I think one issue with soccer is that there is a lack of discrete, measurable outcomes in the game. I read a while back that one of the breakthroughs in basketball analysis came when they started tracking the total point differential during each player's time on court. Because so many points are scored in a game, and because so many games are played in a season, this stat was a fairly reliable and accurate picture of how a player would impact the team's performance (which allowed teams to measure the impact of players who may not rank high in the more traditional stats).

In soccer, you don't have a lot of data points to model against. The number of goals scored is typically low. Because of this, there is probably a higher level of uncertainty and variance in the outcomes of soccer games (and the prediction models as well).