I think it's a good idea.
But on the front page, rather than saying 'we'll post a list of speakers soon' we should be explaining the idea of the 5-minute video messages, asking for people to get in contact with us on the forum with suggestions and ideas, and then when we have a few high-ish profile speakers, we can post them.
Pre-recorded 5-min videos are a great idea because they can be watched at a suitable time for each of the local groups, they don't rely on everyone's internet connections being perfect at the right time, and the speaker can be more focused and prepared - the video can be very simple and direct, or they can add further images/slides to it if they prefer.
I'm happy to help with the technical side of this, eg create guidelines for recording these talks, and if speakers upload their video and slides to the ownCloud (with enough time before the event for me to do it!) I can put them together, add titles and export in the correct format.