You could also take the approach the Django Book originally did. Posting the book online while you write, with editing help from the community and a print version available once complete. I would definitely buy the print version as well as use the web reference.
We are a django shop and I have been concerned about the transition to python 3 for our projects as well as the community in general. Even though I don't think this the end all for a migration, it is a really promising sign. Nice to see this transition starting to occur in the django world.
It is kind of difficult to add JS into this poll in my opinion. I think everyone will have to check js and something else, unless you are talking about using js for the backend as well as front-end. I can't imagine a startup/app that doesn't use js (at least one that is web based)
Although it is great that they are funding Mono and distributing silverlight on other platforms, I hardly think this is for altruistic purposes. They have a history of strongly pushing people towards their OS and platform and then ending support for third party tools (e.g. IE on Mac). I think moving towards something utilizing the power of HTML 5 and Javascript is the way to go long term.