Not really adding anything new to this thread but just wanted to give my $0.02 on Serenity.
I thought it had the best cast chemistry of any TV show I've seen and I would love to see the continuation of the story in any form possible. As far as what story Josh has left to tell that is really secondary to me to simply watching the interaction of the cast. That may sound a little weird but to me great TV shows/movies are defined by a cast that I would want to watch irregardless of the plot line.