The problem I see with it is that, AFAICS, one of the reasons it doesn't currently do it automatically is because it'd waste a lot of writes to the flash that stores that info.
Bookmarks are stored to disk, not flash (they're huge!). This only makes the "too much time" point even more valid.

OTOH the disk is always spun-up when you choose a new playlist anyway, so it shouldn' t be that expensive. I'd guess that we're very likely to implement this sooner or later, though not in time for first release of Pearl.

Peter