The nice thing about 4e, this isn't required to be an extension of any class. It could be a Paragon Path limited to Martial characters that are proficient in Military Ranged weapons. It could then focus on long-range shots and firing into groups. Then it would work with rangers, warlords, and add some ranged options to fighters.
Edit: Which looks like has already been done: http://www.farlandworld.com/paragon.html#longbowman
Sorry for continuing the very old thread.