Wish you would have set up a donation bank or something for this I would have given atleast $100 to help make it happen. This would have so much potential to become a moment of renaissance for a near-extinct genre if it was organized in a good venue, had all the notable guests doing speeches/debating, had good advertisement for a hopefully huge turnout. I'll make you a promise Mods: i am going to start playing the lottery. And if I win I will hook you up with 1 million dollars to organize this 
Edit: Also, I wouldnt realistically expect that you would be able to get all the big names to show up in person in London no matter how many resources you had. But these days with neat inventions like Skype you could probably easily secure a live public webcam interview with people like Ron Gilbert which would, to me, be just as good as the real thing.

Edit: Also, I wouldnt realistically expect that you would be able to get all the big names to show up in person in London no matter how many resources you had. But these days with neat inventions like Skype you could probably easily secure a live public webcam interview with people like Ron Gilbert which would, to me, be just as good as the real thing.