The addition of Longbows would make this game even more awesome than it already is.
This has been asked before.
I dont know if it would fit with the game lore, I mean, in Cairn they already invented guns so it would be very strange to see someone going around with a bow.
Dont get me wrong, I love bows, my main characters in Titan Quest where bow users (Ranger, Brigand), I also loved the Defense mastery, bashing peoples faces with a shield always made me smile lol
Anyways, there has been people asking for bows, spear and staff, maybe they will implement in the future but creating a new branch of weapons is something that takes time and money, having to do the art, the animations and stuff.
Grim quest mod say “hello” guys! 
(except for the bows part)