Unfortunately apart from the name, not much else is known about the device apart from the current rumors. These rumors are saying that the OM-D will feature a 16 million pixel Micro Four Thirds sensor, a built-in electronic viewfinder (EVF), a magnesium body that has been weather sealed and a brand new auto-focus (AF) system.
Given how Olympus currently has a Micro Four Thirds series of their own in the form of the PEN, it is unsure if the rumored OM-D will be replacing the PEN series, adding to the series or starting an entirely new series of its own. The rumors have also outed its launch date for the 8th of February with shipping expected to take place in March, and will come with a price tag of $1,100. As with all rumors, you should probably take this with a grain of salt for now until actual confirmation has been given.