a) in terms of content b] where should it take place c) in terms of additional skills , armor & weapons d) a more combat or story driven DLC e) a combat /story balanced DLC f) at least xxx amount of gameplay hours g) a max. of xxx dollars price h) < feel free to add more> 
a) new beasts, monsters, towns and ruins, as well as new flora, fauna and geography

orsinium, in a long and scenic mountain valley, with settlements along a road strung from falkreath to orsinium to the fringe of the Alik'r desert in NW hammerfell, as well as a brief visit to the ashpit to meet with malacath.
c) none needed, unless the devs can dream up the inclusion of some nifty artifacts (daedric, aedric or even dwemer)
d) story driven. In particular, I'd like to resolve the allegiance of Orsinium (thalmor vs imperium/skyrim and the influence - honorable and/or nefarious - of Hammerfell, High Rock and visiting/spying Akaviri races), the malacath/trinimac dichotomy, and I'd REALLY like to get a chance to absolutely stomp Boethiah.
e) story predominating. The combat will follow. But you should be able to explore more deeply in areas and skills besides combat - magic, espionage, assassination, underworld criminality, diplomacy, business, etc....
f) 80, minimum.
g) $40
There are fundamental elements of a knockout story in an Orsinium expansion that touch upon the basic needs, aspirations, hopes, desires, fears, tribulations, doubts, disappointments and betrayals that are a part of human existence. A carefully crafted Orsinium DLC could, in fact, be shakespearean or even wagnerian in breadth and depth.