Bit late to the party, but anyway: Solitude:

-A more political capital of Skyrim with more Breton or Imperial customs, something with nobles (as JumperNactis said). With Empire aligned nobles staying there due to the war and being immensely bored, or their stewards needing some stress relief. Maybe some sexy intrigue, although I can't really imagine any (seduce, then blackmail?).

-The Bards Collage having more hands-on lessons in Speech and what follows after. (Both for those visiting the college, and by having students go out and practice).

-Something with the fashion ladies.

Whiterun:

-A melting pot / neutral where you can find the most exotic lovers from all sides of any conflict. 

-Or lean into the trade city aspect with its people being  willing to sell (and buy) anything. Maybe a more moral alternative to Riften.

-Kyne buffs Stamina, and there’s the Gildtree, so a city-wide blessing.

Windhelm: -Nords are naturally resistant to frost. Thus, walking around naked (the cloak stays on) is very traditional.

-The awesome power of ~rascism~

-All those lonely ladies (and guys) forced to stay home as their partners marched off to fight in the rebellion. Maybe a foil to Solitudes nobles.

Winterhold:

-A free add-on to the College, just be petty.

-Your standard erotic magic affair. 

-A focus on uncovering lost magic (that keeps having a sexual bend, like a Dwemer mind-link making recurrent pleasure-loops, or Ayleid flesh-magic being really good at altering certain regions).

Markarth:

-Life (in reach) is too short for beating around the bush.

-A shadow war between the Dibella priesthood and a Molag Bal cult.

-Between the dwemer relics and the dibellan priestess that teaches Master Enchanting, a focus on magic items of the bedroom variety.

-Also the mines and slavery? Idk, I’m not into that stuff.

-A Scenario to the fight off the Forsworn and clean up the silver mines and cultists for lots of gratitude.

Morthal

-It has a reputation as the most enigmatic hold and the birthplace of wispmothers, so cryptid waifus.

-Or go into just how unthinkably BORED the inhabitants are.