Actually, I meant this one.
I have a theory regarding Hearthfire.
A hearth is the floor of a fireplace. An ashpit is the receptacle below a hearth that collects ash from the hearth's fire.
Malacath's realm is the Ashpit. Yes, it does seem like a shot in the dark, but allow to explain a few supporting details.
The most important supporting detail is the fact that within the game's files, Malacath has insanely high stats. The files list him at level 100 with over 1200 health, moreso than any other Prince by a huge margin. Why would Bethesda give Malacath such high stats when we can't even meet him? Curious thing.
Orcs have been given a huge overhaul with Skyrim. Bethesda put a lot of time and effort shedding light on their culture. According to the wise woman of Dushnik Yal, Orcs were in Skyrim long before Nords ever set foot in Tamriel. What's even more interesting is that Orsinium has been moved to the Skyrim/Hammerfell border. This is revealed by an in-game load screen, suggesting that it has been rebuilt despite being assumed destroyed according to Lord of Souls. Seems highly convenient.
One of the biggest complaints about Skyrim during its launch was the lack of an arena. Considering what we've learned about the Orcish view of seeking a glorious death, I can think of no better candidate than Orsinium to implement an arena.
I would also like to add that a hearth can also refer to a forge. Forges are obviously associated with blacksmiths and Orcs are known to be the greatest smiths in Tamriel. This is significant because a slew of smithing features could be opened up, such as new weapons like the spear and flail shown in GameJam.
Todd Howard also revealed at E3 once that he would like to see Daggerfall features redone with today's engine. Orsinium was a location featured in Daggerfall...
Considering all of what I've mentioned, I believe that Hearthfire will take us to Orsinium and the Ashpit. I believe it will involve redeeming Malacath. Why? He was once Trinimac, strongest of all et'Ada and Auri-El's champion. It would be in the Thalmor's best interest to recruit Orsinium and attempt to restore Malacath, perhaps via an Elder Scroll. The alternative would be recruiting Orsinium for the Empire, granting Orsinium provincial status.
That's my two cents.