What I would like to see is more of a variety of situations to fight on the roads, as well as more variety of NPCs to fight.
Guilds. Some sort of organized mercenary or fighters guild, thieves guild, alchemist guild, merchants guild.
Increased inclement weather/ seasons? I would love to see snow and epic mountain scenes, more places for adventurer types like more caves, dungeons, mines to explore. Something like a Carpathian mountain DLC would be awesome, complete with foggy pine forests and snow capped peaks.
In addition to this harsher terrain I think there should be more ferocious wildlife. I am sure I am not the only one who thinks fighting bears, wolves, and boars sounds totally rad.
Animal companion.
Crossbows
More blood, gore, dismemberment, impalement.
The next type of DLC which would be so adaptable would be some type of historically accurate horror based around the same time and place. I think the best adaptable horror arc would be that of Transylvanian Vlad the Impaler. It would be the same time and setting with the same type of architecture and castles, except add in the flavour of a harsh mountainous setting with cold, maybe an inclement weather system, ferocious mountain animals, and rumours of the castle nobility bathing in the blood of enemies.