And, to cast the first vote... very, very interested. I think it would provide another dimension of play, provide fresh challenges/opportunities for Fun, greatly increase the realism of the game, and add all sorts of new cool/nasty things to do, including bioweapons and involuntary prisoner testing. I think that "treatment" could include getting special materials/cures- golden salve, unicorn blood, moghopper juice- that would offer fresh incentive for trade, as even a little of these could have a huge impact on your fortress health. I think that the value to the modder community would be invaluable, as expanded disease would include expanded disease effects, which would allow the creation of much more interesting monsters through the use of poisons. Disease could add something to every aspect of fortress life, from defense to agriculture, as well as greatly increasing the richness of world generation as invading armies or caravans carry plagues that influence the course of civilizations. Depending on how carefully fleeing invaders/caravans are tracked, you could even use it as a weapon against enemy civilzations over the course of your own fortress, by sending goblins or elves home with devastating illnesses that will weaken them for generations to come. Disease options would only get more interesting as the rest of the game expands; sometimes breaching hell might result in a special super-plague instead of a horde of demons, or a passing wizard might curse your fortress with a spreading zombie infestation. Finally, I think all of this could be done with relatively little work on the part of Toady, especially if the modders step up to run balance work on a limited system, first.
Finally, all of this would be easily toggleable in the init menu, allowing inexperienced or uninterested players the right to ignore it completely.
Edit: Oh, and we can finally add "Diseased" to the list of dwarven adjectives, on top of "Greedy," "Callous," "Derranged," "Omnicidal," "Kitten-Hating" and "Quirky"