It's a matter of guns matching with the lore, and also fitting with the theme of TES.
Longswords and shortswords belong to the overall family of swords (the staple weapon of TES), so it actually isn't the same idea as guns. Guns aren't part of the bow family--guns are guns.
So, as long as something shoots out, and everything else is cosmetic, then I suppose you wouldn't be opposed to a handheld Bosmer-launcher, hm? Big wooden arms, slingshot loading system, Bosmer for ammunition. Or perhaps something that just looks like a gun, but fires slaughterfish?
Everything has to match a theme, the lore, and must be at least semi-explainable.
I probably wouldn't mind it. Be rather strange, but it wouldn't be impossible to make. It would be hard to find Bosmer's to agree to it, but I'm sure there'd be one. There's always a crazy one.
Crossbows match the theme and the lore.
Guns don't.
Cannons have matched the lore at one point, but only once, and have been explained away as being too heavy (they sink ships) or too unstable (they melt themselves down) for any practical use or further development.
Guns don't.
Muscle-powered ranged weapons and melee weapons (along with magic-powered and Dwemer steam-powered weaponry) match the theme and lore, not mechanical chemical reaction-powered weapons.
GUNS DON'T.
It's all a matter of theme!
Theme? Theme!?
For like the last five posts I've been talking about ways for it to match the theme. Create a small but powerful rune on the inside of the gun, make it so the trigger when pulled removes a barrier that holds the projectile back, and then when the trigger is finally pulled the small metal ball is launched out of the tube.
Use a fire scroll, and when the trigger is pulled it causes the scroll to explode sending the small metal ball flying.
Even the black powder varient which we know as the gun could fit. A tribe of humans who live in the boonies of Skyrim and happen to think magic is evil. They call their cave home, and those who know of them call them the Thunderstick Tribe. How they came up with the tech for guns is beyond you, but there's a quest that you pick up to investigate and get that tech for an intestested indevidual whos trying to gain a leg up in the civil war. Go there, learn how they found and made their guns, and choose to either report back or side with the Thunderstick tribe.
A crazy king, who happens to hate Bosmiers with a passion and happens to be an inventer developes the catapolt, but not for what it was we would think it would be used for. Anything and everything is plausable. That's the great part about writing a story. You can do anything with it. We could find a nuke in a cave that happens to look something like a Fallout 3 vault. Will we? Probably not, but they could do it. It could be explained that the geck maulfunctioned and the inhabitance ended up in a strange snowy climate. As they began to loose power, they left the vault to see if there was anyone outside who would help them only for dragons to attack them.
TES theme is not one thing. Its magic and swords, yes, but its more than that. TES is a world where we can explore, find things that we could never imagine, and be the hero or the villian of that world. Finding a flame thrower one would find in Fallout in a Skyrim cave would be strange. It probably wouldn't fit well with the world. But a TES style flame thrower, where a staff could be held out infront of you and it sends a sea of fire towards the enemy would fit.
Guns could be tweaked to fit the TES theme and yet still be guns.