According to a rumor in the latest issue of PlayStation: The Official Magazine (Issue # 018), Metal Gear Solid 5 will be announced by Konami some time in April or May. We personally think that such a major announcement would be better suited for E3, but we’d like to think PTOM knows what they are talking about.
Speculation suggests a prequel (to Metal Gear Solid 4) featuring Raiden and how he became a Cyborg Ninja, and managed to save Sunny from the Patriots, or a squad based game featuring the newly formed FOXHOUND team being led by Meryl.
PTOM also notes that MGS5 might not be directed by Kojima, but he would probably be involved in some way. They also go on to say that Kojima might have his hands full working on Max Savage, a game that was originally a dream sequence Big Boss had in MGS3.
E3 is only a few months away, so this rumored announcement may be coming much sooner than later.