The character of The Boss could be appearing in Metal Gear Solid V: The Phantom Pain in some form.
The Boss’ voice actress Lori Alan tweeted “maybe so” when asked if she’s in Metal Gear Solid V: The Phantom Pain.
The Boss died at the end of Metal Gear Solid 3. It’s possible Big Boss has a flashback where she appears again to give him some advice or something.
Metal Gear Solid V: The Phantom Pain will be released hopefully next year for the PS4, Xbox One, PS3 and Xbox 360.