As it stands, we have to guess whether a hitter has been unlucky or just bad this season, or whether a pitcher's unusual BABIP is luck or performance. Right now, we know the ground ball/fly ball ratio, and we can figure out K and BB as a percentage of total plate appearances, but the game doesn't appear to give us any aggregated data for whether a "fly ball" was a line drive, or a lazy pop-up. Having a line drive percentage would give us a better indication of whether a hitter is squaring the ball up or not, and whether an underperforming pitcher with a high BABIP is getting pounded or has just been unlucky.
The batted ball data
here is pretty much exactly what I have in mind here for pitchers, and
here for hitters.
Also, being able to track pitcher stats (K, BB, H, HR, etc.) by percentage of plate appearances, rather than just the per nine innings rates, would be a nice addition.