An idea I had, not sure if I should be in Casual or Advanced with this!
The Elder Scrolls: By Right of Blood

EDIT: Actually, after you read this stuff make sure to scroll down the posts! We're making more sense of the RP potential! xD

The RP assumes that:
:: The Empire's allies won in Skyrim's Civil War, Jarl Elisif is the High Queen of the Nords.
:: The Dragonborn did indeed involve themselves with all the 'side factions', they became a holder of many a title, so as to give them plenty of allies - or enemies, perhaps. From Arch-Mage, to Daedric Champion, or Thane to every hold in Skyrim.
:: All missions can be assumed were completed all over Skyrim.
:: The DLCs for Skyrim have also been worked out by this point. The Dragonborn chose to fight with the Dawnguard against the Vampire threat, and Miraak was defeated. If the Dragonborn's player would like adopted/biological children and a home of their own, go for it! Just state what the family consists of.
:: I'll leave it to the Dragonborn's player to decide whether they favoured the support of the Blades or the Greybeards. This is important, but the RP can work with either choice.

The plot:
Whichever path the Dragonborn takes regarding loyalties, to side with the Greybeards or the Blades, Delfine puts a plan in motion to bring a tradition back to the Empire. With questionable methods, the Blades work to increase the Dragonborn's influence, to find them allies and power, and destroy potential threats to their security - their goal: to return a line of Dragonborn Emperors to the throne in the Imperial City, whatever the cost...

Inactive cells of the Blades from all over Tamriel suddenly become active, striking back against the Thalmor. When the Aldmeris Dominion demand action from the Empire, they're frustrated to find that the Empire won't act against the Dragonborn's private army. The Thalmor soon find the Empire's various lords and peoples rejecting them, threatened with execution or imprisonment if they fail to leave Imperial territory.

Whether the Dragonborn hero likes it or not, they're being dragged into a power struggle to take their rightful place as the Emperor, or Empress, of Tamriel. But because of the Blades' less than subtle actions and their results, war once again threatens to erupt all over Tamriel, an Empire prepares to defend itself, and the Dominion fires itself up for war.

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So... That's the base of the whole idea. Thoughts? Anyone interested in playing a part? Dragonborn's available if you didn't already figure that. ;3

If I join I just want to be the leader of the thieves guild

Not quite what I was thinking people might RP in a setting such as this, actually. But, maybe it could work, I don't know.

Then spy master fire the dragon born. Just something stealthy, I always played as a wood elf in game so obviously I was meant to be a thief

'Spose I should bump it a little.
...Bump!

All I'm saying for this is that you're going to need a truly experienced guild member to play the Dragonborn, someone who has a long record of sticking with roleplays to the bitter end. With so much of the plot dependent on a single player/character you're going to also have to work with and rely on them to drive a lot of the plot of the roleplay, as well as give them the creative freedom to do the aforementioned. Playing the main character of this is going to be a big task for whoever takes it.

Subbing to see where this goes.

*This goes nowhere*

I think you'd be better off having the Dragonborn as an NPC, or maybe even have him/her dead following the end of the war. Otherwise that one person is going to be supremely overpowered, and it also takes up a lot of roles that other people may be interested in - such as head of Guilds and whatnot.

However, I am still interested. :)

Dragonborn being dead means so is the plot...
But! That's a much better idea, Roze. What if we just say the Dragonborn settled down, quit all the 'jobs' that came their way throughout the story. So there's new guild leaders, college arch-mage, thanes and all that, but the Dragonborn is still 'related' to those factions as they've worked with them a long time.

As for the Dragonborn's obvious overpower... They're not impossible to kill, and I like to think I'm pretty good at thinking up antagonists. The idea is this extremely skilled and capable person has all the strength and influence to rule Tamriel, so they don't, like.. get shiv'd and keel over like other Emperors that have existed. The power's meant to be their assurance of survival and their way of rightfully claiming the throne.

I'm always interested in an Elder Scrolls Roleplay. That said, I would echo @MiddleEarthRoze's idea that the Dragonborn be an NPC if this gets off the ground. It would be smoother that way.