The PC version was demanded by a lot of people due to the advantages the platform provides and Kojima has listened to them and has made the game possible on the platform. If you remember, when the game was originally titled Metal Gear Rising, a PC port was in the works too but was cancelled. He revealed this information on Hideradio (Japanese)

There's no release date confirmed yet but considering Platinum Games can do a quick job with it, the game should be out later this year. The PC version should allow people to play with a higher visual fidelity, however, there won’t be any frame rate advantage since the console version already runs at 60fps.