A bit tangential to the subject, but...
What could be cool is a spell database in Next' DDI, where a DM could edit spell lists for the current PCs of her current campaign, by adding, subtracting, mix&matching, importing the Setting (FR, Dragonlance, Eberron, ...) settings, copying and pasting from friends from their kool social network supported by DDI...
It would solve some problems of what is core/allowed and not, simplify bookkeeping, etc. It would enable plenty of cool new ideas (and sacred cow sacrifices ;-) ), but of course, enabling, designing and balancing are quite different issues...
By the way, such a database would work miracles for a bestiary, enabling a DM to tailor the monster list and the individual abilities (and fluff !) of each monster entry in her homebrew setting (even the monster look, if enough art were to be incorporated in this uber db).