Idea 1) would see a political RP set in the Empire, with players acting as the vassals of the Emperor, or the vassals of those vassals, or whatever degree of power potential players would desire. I'd be playing as the Emperor (read: GM) and King of Cyrodiil, the central realm that encompasses the Imperial City and some area around it, at least for as long as the character I'm RPing remains Emperor. The RP would begin at 4E 246, when the already mistrustful councillors would be split apart by an argument involving Skyrim which, despite being composed of several independant nations, is seen by the Emperors and their vassals as the possession of the Cyrodiilic Empire. It would stem from the fact that Winter Hold, the old rival of Solitude, has stepped out of the Kingdom of Solitude that was formed along the northern coast of Skyrim following the Dawnstar Union of 4E 92 when Winter Hold agreed to become a part of the Kingdom to help fend off the Kingdom of Whiterun encroaching upon both Solitude and Winter Hold; having broken the union, the newly crowned King of Winter Hold has also declared war on Solitude. Thus, the Emperor decides that the Empire needs to step in and stop the squabbling between the two cities, as that leaves no counterbalance for Whiterun in Skyrim and allows the Kingdom grow powerful enough to ignore the Cyrodiilic Empire should Whiterun swallow up both Solitude and Winter Hold.
However, the councillors are not really agreeing on whichever should be supported, and the Imperial Council is split into two, one side supporting aiding Solitude in regaining Winter Hold, and the other side suggesting deposing Solitude and instead leaving Winter Hold in control of the northern coast. Since war is prohibited under thread of Imperial Ban (banning of the agressor from the Council, with his/her vassals released free of their oath and promised the former councillor's power if they manage to dispose of him/her before the Imperial Army arrives), the RP would circle around political intrigues in the Council, with cloak and dagger things to try and dispose of your opponents in an attempt to become the next Emperor.
Idea 2) would be very closely related to the first idea, taking place at the same time, however dealing with the conflict of Winter Hold and Solitude after the Dawnstar Union's terms were broken and war broke out. It could be a lot of things, really, there's no clear way to define the RP's genre - it has the potential for political intrigue, to a lesser extent than the first idea. Solitude would be the larger power, thus the players on the Winter Hold side of things would be encouraged to try and break up Solitude's power, since Solitude would be split into two sub-factions, with the city herself and Dawnstar, the King of which would probably want to exploit this situation and gain independance. Treaties could be also made with external players, i.e. Kingdom of Whiterun, although that is a risky bet as Whiterun is bent on uniting Skyrim. Warfare would take place, in the form of many small raids and the occasional larger engagement, which would be fairly rare, as neither side has manpower available in large numbers. The raids would also allow for an adventury feel to the RP, since they'd range from a handful of soldiers and a single ship to ten or so ships and several hundred men. In this RP I'd be acting as the King of Whiterun and a neutral ruler at the beginning; I'd also be the GM, making some events and moving things along if all else fails.
Speaking of events, they'd make the two RP ideas overlap, as, for example, rather unexpectedly the Empire may invade Skyrim in a Drag Nach Osten-like thing and screw things up a bit or a lot. There'd be other sorts of events, and a few new factions may come into play along the two main factions (since I don't intend to have anyone else than myself in Whiterun as the focus is on the north coast and not entire Skyrim).
I haven't worked a lot out besides a loose timeline for the thing; however, I am considering having gunpowder in as a recent discovery, to give something interesting to play around with. In the case that gunpowder made it in, it'd be mostly in the form of small cannons mounted on the Nordic boats, maybe some odd arquebus-armed soldiers for the North Coast RP; for the Empire RP, I'm not as sure since warfare won't be a main focus, however probably heavier cannons and pike and shot formations as a whole new, experimental concept not yet employed in major battles. In any case, gunpowder troops wouldn't be fielded in large numbers, mainly as morale droppers, and the combat would stay close to ye olde hack n' slash.
So, comments, suggestions, anything? I want to know which of the two would be in more demand before I expand any of the two a lot.