Coleman is Codemasters’ Chief Game Designer, and works exclusively on the DiRT games, something that’s reinforced by his message. “Commence your speculation,” he wrote, before adding the “#DiRT” hashtag.
Not a great deal of speculation needed, then, although of course this could end up being anything at all. It’s unlikely to just be DLC – it’s been a year since we first saw DiRT 3. That rally car’s hardly inconspicuous, though, is it, and it’s clearly something to do with the wheel setup photographed in one of the other (Instagrammed up) images he Tweeted.