Today Treyarch announced that they will be adding modding and map design tools to Call of Duty: Black Ops III. These tools will be available exclusive to the PC version of the game and directly supported by Activision. Along with the tools will be included dedicated servers for hosting modded game modes and user generated maps. These servers will including a browsing feature that will allow you to access player maps and mods from all over the globe easily. It sounds like they're going for the feeling of the Steam Workshop in accessibility to player-to-player sharing of custom content.
Call of Duty: Black Ops III releases November 6th for PS4, PS3, Xbox One, Xbox 360, and PC. The alpha test of the modding tools is set to debut March of next year.
Source: Treyarch Blog