Leave Bethesda alone. Something as simple as "WE WANT CROSSBOWS" is not worth wasting their time with. They've already taken into consideration whether or not they're going to add crossbows and a bunch of email harassment isn't going to change that at this point.
I think an e-mail is a waste of time (and annoying to anyone having to sift through it) but it's certainly worth posting about. Obviously, whether they are in the game or not hasn't been confirmed yet, but if they've made the decision not to include them, I think it's important that people disagree.
Anyways. The thing with crossbows isn't always power, but accuracy. Since you're not holding the tension of the bow string yourself and since the bolt is rested on a flat surface, it's easier to hit targets than with a traditional bow. Now, the most powerful crossbow IS probably more powerful than the most powerful bow, because humans just can compete with mechanics.
But, I think any one-handed crossbows would actually be quicker to load, and could be held off hand with a sword. Basically it's a one hand operation to [censored] the string into the lock. Obviously, the range and power is incredibly diminished. Good for poison or supernatural creatures if you use silver bolts and enchantments, but almost useless against people in armor.
Also, repeating crossbows like the Chinese had. Two hands, extremely low power, about 6-10 shots. Also best used when combined with poison.