We've absolutely no idea what it is, but we've included a series of messages from the Metal Gear mastermind for your convenience:
Have to give priority to another lines scenario etc., so now I cannot work on the devil project and writing.
Worked on my devil project a bit after lunch. An experiment went well. Plot adjustment. Additional project. Phew.. now another line.
Kojima teased his "dream project" during Sony's NGP announcement conference, hinting at some kind of console/portable crossover. The video game legend suggested we'd learn more at E3. Could Kojima's "devil project" and "dream project" be connected?
We've no idea. Only Kojima could manage to confuse us this much though.