Absolutely zero information has been released on the title (at least officially) but what IS known is that the game will be a port or possibly remake (probably closer to an update though, really) of Metal Gear Solid 3.
Exactly which version of the game is being remade is a mystery, although one would hope that it is the “Subsistence” version, which included many enhancements over the original PS2 version, including a fully 3D rotatable camera. The PS2 release of Subsistence also included lots of other extras like the competitive multiplayer Metal Gear Online and ports of the original Metal Gear and Metal Gear 2: Solid Snake, but it’s doubtful that these will carry over to the 3DS version (the classic ports didn’t even carry over for the PS2 “Metal Gear Solid Essentials” collection version).
Here is a video of the game running on the 3DS, and as you can tell the graphics are great. Sadly though, the stereoscopic 3D effects don’t translate to video.
And here is an interview with Metal Gear Solid creator Hideo Kojima regarding his thoughts on the 3DS.