A Solid Snake Sword, playable Sam, and Bladewolf
First, there's confirmation of a side-scrolling beat 'em up VR mission that has Raiden going full fisticuffs, in addition to a Dwarf Gekko-centric mission.
The next bit is a DLC weapon called the "Soul Snake Wooden Sword," that has the soul of Solid Snake embedded in it, and speaks Snake's voice when you use it (crazy!) -- it'll come with the VR Mission pack.
Lastly, there seem to be two extra missions involving a playable Sam, one of the main antagonists of the game, and another involving the Bladewolf, Raiden's trusty robot sidekick.