That's pretty cool! But only useful for the few of my friends that would know how to run a perl script (and have LaTeX installed) unfortunately LaTeX is a rarity at Swedish schools and I need to make it super simple and install-free to make some of my classmates use it.
Thanks! You could use that script yourself to keep a copy of the pdf live on the web. Then your collaborators could edit the LaTeX on etherpad and keep re-fetching example.com/foo.pdf for the pdf of what they're editing. If they're not hardcore LaTeX people then maybe that will suffice for them.