Crossbows aren't dawnguard exclusive! They have been around and widely available since at least the time of Nerevarine. They weren't in oblivion because dumbing down was bethesda's first design priority and they're back now because it's high time bethesda got the memo and started ADDING features instead of removing and finally put them back in.
They will probably be craftable, probably make it into vendors and probably will be in loot lists too. Either bethesda does that or mods will but it just NEEDS to be done. If not they will look slapped on and out of place.


