Well, at first I thought we could end the whole crossbow debate now, but it seems we're not certain after all. If crossbows do appear, though, I hope they're implemented better than in Morrowind, where they always felt kind of half-hearted to me. They were basically the same as bows in terms of gameplay mechanics except you didn't need to hold down the attack button to get powwrful shots. Beyond that, the differences seemed to just be cosmetic, and the lack of options available just made them feel kind of pointless. About the only worth while thing they really added was that they provided modders with the necessary animations and mechanics to make custom crossbows. If they appear in Skyrim, since Bethesda seems to be training to make the weapon types each feel distinct, crossbows would have to be too, if they were used. Having them just be bows you hold differently just wouldn't cut it.
No matter how much Crossbows would or wouldn't be part of previous lore, it doesn't mean it has to be in the game just because some crossbows would have been left behind by the Dwemer and no matter if crossbows were in Morrowind, I don't think it fits Fantasy in any way, it's just one step away from hand portable cannons (hand guns) and muskets, or at least that's how I think about it. There will always be Morrowind fans who scream out loud that they want to find crossbows in Skyrim (light sabers in LoTR), but I'll just get puzzled by them none the less.
I fail to see how you can say crossbows don't fit the setting. Disregarding the fact that they've been in the series before. It's not like crossbows are a modern invention, these aren't guns we're talking about here, crossbows are pretty standard fair among Medieval weapons, and they've appeared in many psuedo-Medieval fantasy settings before, I don't see how they're out of place in such a setting at all. Now, that doesn't mean you have to want them, of course. But "They don't fit the setting" isn't really a valid argument against them here, I think.
And in any case, as has been said, just because the game takes place in Skyrim doesn't mean EVERYTHING has to be Viking themed. It may be the predominant theme, but other cultures in the setting should realistically be represented as well.