I must say don't read anything into my guess. The only thing that actually has any weight in my post are the mysterious 8, 10 and 15k tags on the Active.com site for the 2012 marathon relay. In all seriousness, the web folks tied to the runDisney folks are notoriously bad at cutting and pasting between websites, etc. Take the ability to find the waivers a week early, the fact that I found pricing 5 days early, etc. This leads me to believe that these race distances are under heavy consideration within the organization.
It would not surprise me to see a weekend of endurance races ranging from marathon with relays down to the 8k/5mile or 5k. A marathon may be long for April but we run them in April along the Gulf coast. With Elite coming out with a twilight/night marathon, it would not surprise me to see a night marathon. But then everything in the paragraph is a pure guess.
I still believe April is the date just to give a full 12 months of hype and build up for the race. But it could be anywhere from February through April given the history of new race announcements. For a while Disney was announcing ten months out. That would overlay existing races so maybe that is not a real option, unless they can one of the late winter races.
Now to add a little more to the conversation, one of the issues with a marathon or half is that Disney seems married to running these races through MK. What draw is there to running the same course in a different time of year? I think there has to be conversations on how to change things up. Running the same course may not create a high demand, especially in a hotter season.
There is a brand new course that has never been raced starting from the Race car track and working back to Epcot. This course was created for the inaugural Princess half. Plans were scrapped once feedback on not allow princesses to run through the castle was heard. There is also an older marathon course that is completely different from the current venue. The venue would work better for a night course than a day course as MK was later in the race..... Not a great thing from the accountants perspective... that's why the race does everything in the world to get racers launched before 6:20 - allowing enough time for all to get through MK before park opening. There are other issues with the older marathon course; like part of the early course ran past what is now Boardwalk. That is not going to happen easily.
So, like everyone, I am anxiously awaiting real news.