Well, IF we can believe AintItCool.com, they've known for a while that John August has been working on a script. So, if that's true, the fact that he has has indeed been going unreported until yesterday. At the time that Marcy mentioned she would announce the screenwriter's name, I'm sure she was quite sincere about it. However, one place I think we disagree might be that if Marcy was, say, told off the record about August and Burton's involvement in the Depp/DS film and she was asked to not circulate that news in SG or her online updates because TPTB decided they want to make the official announcement at the Fest, there would be absolutely nothing wrong with that. Originally she may not have been made aware of their plans or they may have simply changed their minds after she'd already said that she'd report the screenwriter's name when confirmation of it developed. IF TPTB made a specific request of her not to say anything, there really isn't much she can do.
Of course, I don't know if that's the case. Now that the news is out, an SG update on the subject of August (and Burton) could be being prepared as I write this and it could come out any minute. But my original reply to you was simply meant as a caution that there's also a possibility that that isn't the case and we probably shouldn't get upset if nothing surfaces from SG until after the Fest - especially if the plan is to make any and all official announcements at the Fest.
Also, unless things have changed since last year at this time, there really is no such thing as DCP anymore - at least not in the way it had previously existed. Its offices were closed down after DC's death, and David Kennedy, its former president, became an independent producer. (I believe there's still a contact phone number for people interested in DCP's catalog of already produced material and the rights to such, but there's no longer any day to day operation.) As Variety reported last July, it was DC's estate that negotiated the deal with Depp for the rights to make a new DS movie - but they might not even have much of a say in how the film is made because that seems to vary from rights deal to rights deal...