While mainly addressing the way the plague is being handled, this thread also mentions testing a system that will serve as the basis for forum-based quests and such. This is not identical to what you propose, and they have not yet released details, but it could potentially serve as another avenue for CDQs and such as you suggest.
Director's Cut: Additionally, even without whatever system Dorg alludes to, the forums have become crucial in the last few years to progressing events. I would argue that the day a time limit was put on the EC/WLDQs was the start of falling back to the forums as a means to work out conversations and distribute information without the IG clock running. By the time later epics were running, if you weren't exchanging PMs, posting in your forum, meeting IG without a DM, etc, you were not making full use of your time.
Long-running quest series also get their own forum for people to RP in and wrap up events, or for campaign-specific rumors and info to be posted... Player-run establishments like the Silver Buckle and the Leringard Arms have their own forums as well, that we use to RP between characters now and again. Lastly, each deity has their own forum that can be joined as well, which, depending on the deity have been used to hold meetings with fellow worshipers. Sometimes DMs will use any one of these to start an RP thread going that will later translate to IG events. One example is Ravemore, a DM that would typically start a thread with his events, take RP and dice rolls for a given time, and then conclude with a single session IG. He and other DMs have also posted bounties for special enemies they've placed... you get the idea.
My point was just that I'm not sure what is being tested right now, but they are definitely there for people who want to take the initiative and don't mind the sometimes weirdness of being in one place on a forum thread and somewhere else IG
I do like the direction of the Black Plaque quest line that you pointed me to and it looks like that could lead to what I'm suggesting (or at least have the same general idea).
My suggestion is more in the lines of CDQ's where the player him/herself leades the discussion with a goal in mind for their character and the DM's and other players get involved as seen fit (In the other server other players didn't get involved unless invited by that player, much like how a CDQ works here). This could basically replace the CDQ with a more forum approach toward it, allowing the player to broaden his horizons that can sometimes be limited in game. Also as mentioned it means the character can progress the same way they would want to in a CDQ, without working out the time constraints with other players and DM's, but instead reply appropriately as the thread expands (Basically a better use of everyones time). This can all then become an in game CDQ to finalize the players desire for said character, or simply finish in forum.
Something along these lines is already in the works. What is happening with the Black Plague right now is, as we've stated, is the first part of this and firmly a work-in-progress. Details on this first pass will be posted very shortly, but this first pass is intented to test only certain aspects. There will be more to come as we test, refine and progress.
As Acacea noted, this sort of thing has been already used pretty extensively. What we're looking at, however, is more of a formalization of using these forums as an alternative to in-game RP with some structural elements to keep events moving forward while providing for some methods appropriate to the medium.
Whether it ultimately takes the form the OP described above or not, there will be something that comes out of this effort.