How would you feel about guns in TES: 6? Now chill for a second, because I'm not suggesting a AK-47 with an acog scope, I'm talking about muskets and maybe a flintlock weapons. It is in no way impossible as a technological advancements in Nirn. Especially, with all the magic which could jump start any technological innovation. I mean, the Dwemer have robots. I don't think a little tube of wood and iron with some gunpowder is too farfetched. The earliest guns have been traced back to the 13th century and in fact the Ottoman Empire in the 15th century used firearms as part of its regular infantry. So, as a historical analogy could make sense. Could be kind of refreshing to see some more technological advancements like this in TES: VI. Under the assumption that TES: 6 is set after Skyrim.
Firearms could have its own skill or fit in as a branch under a marksman skill (which would include archery, crossbows and firearms).
Firearms ammo would be much rarer and much more expensive and reload be vastly slower than a crossbow. But of course, a rifle would dish out dish out most of the damage. Imagine a pirate in Stros M'kai that you have to take out and you think "Aw yeah just a normal bandit." then he unleashes an attack from a flintlock pistol, dropping you to half health and now making the fight a lot harder.
A musket would be a weapon you would use to say, take out a mage with one shot because it has got higher damage than a bow or a crossbow.