it is an interesting idea and it is also feasible. the wire on the crossbow could be pulled back using a lever action mechanism like the model 1887 in cod games and it could load from a top down magazine using gravity to drop the bolt into place. the downside of this weapon is that the clip would have to be replaced every 5-10 shots.
Problem is that you would not get enough power from the lever action, in the rifle you only has to move the bolt back and forward to reload, with an crossbow you has to use a lot of force to draw the bow again. Yes you could use magic, perhaps some of the dwemer dynamos but in this case you could just as well have it as an autoloader.
No it's not an insane weapon design. I had the idea of something like the gatling laser in fallout but using six magic staves who rotated and shoot different spells downrange.
People was discussing airplanes and helicopters in Fallout 3, my idea was an mini nuke powered one, think an combination of an orion spaceship http://en.wikipedia.org/wiki/Project_Orion_(nuclear_propulsion) and a pogo stick