It just wouldn't have the right feel for Skyrim,or any other ES game imo.
It wouldn't be too much of a stretch, but since no one alive knows how to work Dwemer machinery, they would be remarkably rare since they could not be reproduced, and probably likely to explode in your face since they are so old. It would also mess with gameplay, and doesn't particularly fit in the game well anyway.
Crossbows won't be in for gameplay reasons. I don't personally have any problem with them being in; they've been in before and were fine, but I would never use them, so it doesn't break my heart that they're gone.
Slings could be interesting, but I've never seen or heard of anything like that in any TES lore or games. I'm not sure it would work too well with the gameplay, either.
I would personally like to see the rebirth of throwing weapons. Not even as part of any skill, just some things you can throw at enemies to soften them up when charging into battle on a skirmisher-type character.