Recently, a casting list with details for Black Ops III was leaked.
The commercial casting, as it is called, had Alex Mason and Edward Richtofen listed, to get actors who look similar to play the role in Black Ops III.
- "A male Caucasian and Marine Force Recon Captain in the age group between 25 and 40. the main playable character in Call of Duty Black Ops and the main playable character in the 1980s missions of Call of Duty Black Ops II."
- — Casting Details for Alex Mason
- "A Caucasian male between the ages of 25 and 40; “a mad scientist type, and psychopath with desire for violence.”"
- — Casting Details for Edward Richtofen
So this suggests that the game might be between past and future again, just like Black Ops II.
This confirms 2 things: Zombies Mode and whether or not these characters will be playable, they will 100% be used in some way in Black Ops III, even if its just a mention or making a brief appearance.