can a program send a hint to preload?
* a media play tell preload what files were on the play queue.
* slide show program could tell preload which images were coming up soon
* after logging in gnome could tell preload which files are in the recently used files list.
* nautilus window could tell preload to cache subdirectories
Those kinds of prefetchings should be done by the application itself. There is the posix_fadvise() syscall to exactly do that. Preload is about predicting... When you know, just do it.