I don't know how complex the rights/legal situations might be with some of these games, but based on the GOG.com wishlist, there are thousands of people who would like to buy Activision-owned games that still have not been released on GOG: Vampire: The Masquerade - Bloodlines, SWAT 4, Soldier Of Fortune, Empires: Dawn of the Modern World, Heretic II, Emperor: Rise Of The Middle Kingdom, and various Sierra games still not available on GOG like Freddy Pharkas and Willy Beamish. I recognize there's not a ton of money to be made off re-releases of these titles, but it would boost relations with people and make many happy to be able to play these again DRM-free. (Plus, my assumption is GOG would do all the technical work getting them compatible with modern machines.)
Since it seems both Activision and GOG will have representatives at GamesCom, please be open to discussing this situation with them.