A point to consider is that at least two classes gain immuity to disease, the paladin and the monk. Those abilities become pointless if the devs fail to implement a meaningful duration and progression for diseases in general. Additionally, the diseases in the Forgotten Realms are rarely as simple as a cold. Lycanthropy, mummy rot, and other potentially worse than fatal magical diseases also exist. Granted, I don't expect them to impelemet every possible disaease one can catch in the Realms, but I do believe the effort would improve the game.
