I was running through the second season of Voyager, and has a few ideas regarding the Vidiians when they should make their apperance in STO.
In the episode "Think Tank", it was mentioned that the group had found a cure to the Phage for the Vidiians. This could have been a ruse, but it could have been true. If it was true, that doesn't mean that it was possible to administer this cure to the entire race. Perhapse one of the items required for the cure is rare and hard to find such that a mass inccoulation of the population is impossible.
Take the line that the Vidiians are still suffering from that disease, it follows that many mission would involve ships harrasing the player, trying to harvest organs. Granted, this would get monotonus after a while, but the interplay of how the Feds, the Klinks, and the Romulans react could prove intrigueing.
Another track could follow that there are two groups within the Vidiian Soldality. One group may have had ancestors whom practiced strict barrier nursing proceedures (similar to the treatment of the Ebola Virus) that an elite few families never contracted the disease. A mentality of "purists" who have never recieved transplants conflicting with those whom they precieve as having "polluted" DNA. This could get into a story line involving the evils of Eugenics and "genetic purity" without having to involve Human augments, or Khan.
There is a possibility that some races such as the Romulans or the Klingons may react to the Vidiians' organ harvesting and the Phage by trying to exterminate the Vidiian race. As Klingon tissue is resistant to the diseage, they would be particularly choice targets from the Vidiian perspective. A power play could ensue where in the Federation is drawn into the conflict, torn between aiding those asking for protection, and the Prime Directive keeping them from interfering with the interaction between soverign galactic powers. The Klingons would be motivated by revenge for the murder and theft of body parts. The Romulans might be more motivated by fear that the disease would adapt and jump from the Vidiians to their race, hence attempt to exterminate the Vidiians before that could happen. Alternatly, the Romulans could offer the body parts of those they conqure in exchange for the allegence of the Vidiians.
In short, there is great potential for much role playing and storytelling involving the Vidiians. I would hope that they would be added to the game.
I think you missed my point that administering a cure to the Phage on such a massive scale might not be very practical. While the smallpox vaccine may have been successfully done, how many other diseases have been eliminated?
To the point about being so far away, the Hirogen were in the Delta Quardent about 50,000 to 60,000 light years away. With the implementation of the Transwarp network, it is entirely possible for a ship from the Far end of the Delta Quadrent to travel to the Near Alpha and Beta Quadrents in about a couple of days; the same amount of time to travel across the local sector blocks.