I'd love to see a live-collaborative LyX... I'd like to see a live-collaborative everything, but most open-source codebases make so many assumptions about a single editor per buffer/document, or a single cursor per buffer/document, that adding collaborative functionality is a gargantuan and very application-specific task. I don't think it's even possible to find a general strategy for making the necessary modifications, but if someone were to figure out how, they'd be the most in-demand consultant in tech, that's for sure.