Use Iroh and gossip to sync remote viewers to presenter. We could show a QR code to let folks access the presentation from their device, and watch along on their phone. Useful especially for getting information on slides that you missed.
It should pair well with the BroadcastChannel sync mechanism that already exists, but we might want to consider extra "room" information, e.g. which slides have been revealed so we can prevent folks from scrolling ahead.