My immediate response when I saw the topic thread was 'oh dear, too overpowered', but realistically I think it could work, especially if the red 'target area' was visible to both teams. As you said, it takes a long time to fire and it could be a great resource in removing things such as Hemorrhage/Abridged shotgun-objective-campers. I don't think it would work on maps such as Boneyard, where there are several major spawn-points close to each other.