I don't think we'll be visiting any other countries in Tamriel as part of the second expansion pack for Skyrim. This is Elder Scrolls V:
Skyrim, not Hammerfell or any other.
Nor do I think we'll play a part in deciding the fate of the Empire/Emperor's throne since no-one has won the civil war yet, it hasn't been recorded in TES lore and is still ongoing. Things like that will probably be decided when the next game is released, and we'll have a summary of what's happened since 4E 201 when the events of Skyrim happened (Ulfric killed the High King, civil war broke out, Alduin returned and is killed etc).
It's possible that the storyline for Hearthfire, assuming that's the name of the next expansion, is linked to necromancy, if the rumours I heard are true. Before Dawnguard, vampires in Skyrim were pretty boring and were no more than hostile mages to me. Maybe the same will happen with necromancers, and they will have awesome powers instead of boring raise dead body spells, and the player can delve deeper in to necromancy and use those powers, or try and stop the necromancers, but then that would just turn in to some sort of recycled Dawnguard so I don't know. But there is a chance the storyline of the Hearthfire expansion is related to necromancy somehow.
Maybe the great tiger-dragon, the biggest dragon on Nirn, Tosh Raka of Akavir, who has plans to invade Tamriel, will actually attempt that, and it will be up to the Dragonborn to stop him. If that's the case obviously it'd be more in-depth than just 'stop a dragon from fluffing plops up'. Akaviri weapon/armour design seems to resemble that of the samurai. So maybe Tosh Raka would be a Chinese style dragon as opposed to a Norse one, something like this
Then again the whole Akaviri dragon thing doesn't really link to the name Hearthfire.
I guess only time will tell. There are also rumours that we will be able to purchase land and build our own houses/buildings in the game as part of the next expansion, which if it's true will be awesome.