75th Kojima Productions Report - 4 more characters to come

Well, The Packers won which means Ryan Payton has to reveal something after getting permission from Konami. In the podcast he says that three projects have begun at Kojima Productions, and his original plan was to announce one of them on the podcast, however he sadly could not obtain the permission.
He did however mention that there will be 4 new characters in the game that haven't been shown in trailers or screenshots to date, 3 of which are returning and one of which is a new character to the series. All four characters are said to be "major" and will have full voice roles and will play a major part in the game.
Perhaps one of which could be Big Boss, who is speculated to be the old, skinny character with the eyepatch in this piece of artwork. Another one of the characters in the game will most likely be Mei Ling from Metal Gear Solid 1 who has been mentioned earlier but has yet to appear in any trailers or screenshots.

Source: Kojima Productions Podcast