Maybe this idea will catch an experienced modder's eye, as I have not the skill or the time to do this myself (yet).
I've been thinking of an alternative ending to the Civil War: what if the player wins? Bethesda didn't give us a clear-cut answer to the problem of who should rule Skyrim. While every character I play hates the Dominion and kills Thalmor gladly, neither Elisif nor Ulfric are particularly attractive choices for High king/queen to me.
There are a lot of lead-ins to the player getting ultimate cosmic power in the story-line, too. The fact that Talos (Tiber Septim, himself) was of the Nedic Peoples of Atmora and therefore could be claimed by the Nords, Imperials, and Bretons and was Dragonborn pretty much opens the door for any race player character to rise to any throne all the way up to Emperor/Empress.
As a matter of fact,
Spoiler
So, why not take that power? The PC is obviously more powerful than Gen Tullius, the Penitus Occulatus, and Ulfric combined, and is a hero to the people. The end result, in my mind, would be the ability to choose who is worthy of being Jarl, instead of having some folks shoved down our throats because they were more loyal to one side or the other.
For instance, Laila is as self-serving, turn-a-blind-eye, as Siddgeir, but you get one or the other. Your opposite choices are Maven Blackbriar, in bed with both the Thieves' Guild and the Dark Brotherhood or Dengeir, only slightly less paranoid than Esbern.
Personally, I'd rather have Mjoll as Jarl of the Rift with Aerin as her Steward, rather than either Laila (and her steward Anuriel, who is clearly a Thalmor plant) or Maven. As for Falkreath, if I had to choose right now, Thadgeir would be a better than either Siddgeir or Dengeir.
These are just a couple of examples, but I'd love to see it set up the same way as choosing a steward for your own houses. If your disposition is high enough with a character, you can offer the Jarl's seat to him/her. Although the role-playing aspect would keep me choosing at least from among the people of the cities that are the seats of each hold, I would ask a modder not to put limits on such a choice. Simply because I know everyone doesn't feel the same way I do.
I'd prefer no limits on race, either. Who wouldn't love to see Ulfric unseated by a Dunmer, or even an Argonian?
I don't see how this would be impossible, as it would only affect the very last bit of the Civil War questline and can happen after one side or the other has technically won. A quick coup while everyone is in disarray wouldn't be unprecedented, especially while the victors are still singing the PC's praises. On the other hand, maybe the PC will have the opportunity to perform a few "Witcher-style" Jarl-slayings to get things fixed up?
One last feature suggestion: taking down the Thalmor Embassy the way the vampires took out the Hall of the Vigilants, then, perhaps, rebuilding it as the best fortified player home in Skyrim.
Anyway, if you've read this far, you can see my skill is in telling a story, not putting it in game. I'm just hoping someone with the skill thinks this is a good enough idea to make it happen. Otherwise, hope you enjoyed the read.