I don't know if this is already a feature in DF, but it would be nice if it could place files in a certain order on the disk, instead of just contiguously.
System files come first, followed by files executed as Windows loads. Then comes commonly used applications such as web browsers and office apps, then games and movies.
Rarely used non-system data should come last.
Free space could be allotted to prevent loss of this system over time controlled by an active program (Perfectdisk uses such an approach with SmartPlacement, though I don't know what it does exactly).
Of course, such programs probably aren't the best for peformance with system activity of any significance (those non-gaming office people probably don't notice any difference in performance), so perhaps it would be best to allow the degradation of this system for maximum write performance and have it be fixed by regular defrags.