With Dawnguard accounted for and well on its way, Bethesda may be preparing for the next wave of Skyrim DLC. ZeniMax Media has filed a trademark application for the phrase "Heart Fire", a phrase familiar to those well versed in all things Elder Scrolls. It's unknown if the filing actually has anything directly to do with Elder Scrolls or is a whole new game all together but given its meaning to TES, it's doubtful it could be anything else.
It should be noted that there are two different spellings of Hearth Fire. "Hearth Fire" is like that of the tome “2920, vol 09 – Hearth Fire”, a book within the Elder Scrolls universe that adds to the Conjuration skill, while the spelling Hearthfire (sometimes Heartfire) is a month during the fall of the Tamriel calendar. While the book undoubtedly takes place during that time, it's unknown if there is a reason for the distinction.