Here’s the exact statement that the man himself posted in the forums of The One Ring:

In a few days there will be a BIG announcement (big for me, at least) that is not-Hobbit related. BEFORE anyone starts wondering the usual “how does he have time?, Is this detracting form The Hobbit?” etc It is a project that started over 2 years ago, before The Hobbit and will render fruits in the mid-term, not intruding on my Hobbit duties. Rest assured. The key letter is “D”

Interesting news it is, below here are some theories as to what htis might mean. REMEMBER, these are just THEORIES, it hasn't been confirmed just yet.

Just last week we found out that Nikolaj Arcel has been tagged to direct Deadman, the DC comics adaptation that del Toro is producing. That’s three Ds, at least (throw in another if you count producer Don Murphy, maybe even another if you expect Doug Jones to take the lead role, as many do) and this film also fits the “over 2 years ago” clue nicely, with Peter first reporting on the film in 2006. But… is this really a big announcement? And would del Toro really try such an elliptical tease when he’s talking about a film that was in the trades just days ago?

Even though del Toro has a famously full slate of projects in development, it has been suggested several times that his first post-Hobbit picture will be an adaptation of Dan Simmons‘ novel Drood. It’s a historical murder mystery narrated, and most unreliably so, by a fictionalised version of the novelist Wilkie Collins. Collins embarks upon a journey into a threatening underworld with his friend Charles Dickens, in pursuit of the mysterious titular Drood. Though I’ve not read the book myself, those I trust have only positive things to tell me about it and as soon as I stop being lazy, I’m going to leap right in.

The last possibility is another comics adaptation. Back in 2008, del Toro told Empire magazine that he’d spoken to Neil Gaiman about a possible adaptation of Marvel’s Dr. Strange. Gaiman later clarified that he’d spoken to the big man about the job and was very excited, adding “I would love to write Dr. Strange. It would be absolutely one of my dream jobs, a Dr. Strange movie”.

So that’s a D for Dr. and, given the recent Marvel maneuvres, a D for Disney too. Kevin Feige at Marvel has said “as we start putting together our film slate for 2012 and 2013, I would not be shocked if we saw Dr. Strange on those lists”. The timing seems right, I think. del Toro could be ready to film Strange in early 2012, perhaps? That would give Gaiman plenty of time to get the script in shape.

I remember reading a while ago that he was really interested in the Drood novel. I don't remember where I read it, but that seems like it would be a good fit for him and I'm kinda hoping that's what the news is. Although I'd be fantastically happy with Dr. Strange as well.