According to the Konami's press release Hideo Kojima will demonstrate Metal Gear Solid 4 at the Leipzig Games Convention, along with some other surprises.
Konami will also show the new trailer where Kojima will show some of the new stuff, and where he will also reveal some exciting news about the Metal Gear projects from Kojima Productions.
In the words of the great Hideo Kojima himself "When I last came to Leipzig, I promised fans of Metal Gear Solid they would be able to see a playable version of MGS4 – and, to celebrate the special nature of the occasion, I can confirm, that I will bring a special guest with me. I love the enthusiasm European games players constantly show towards our titles, and look forward to showing METAL GEAR SOLID 4: GUNS OF THE PATRIOTS at the most important European gaming event of the year."
The mystery of the special guest still remains.