User blog comment:Jimeee/Hearthfire confirmed as the latest add-on. Official trailer./@comment-3323650-20120831121329/@comment-4976111-20120901193414

They will. They mentioned early on that they'd be working on 2 very big DLC's. I presume Dawnguard might be one of them. Hearthfire's just a small thing inbetween. If I had to guess, there's one more huge one coming soon.