The idea is very interesting But you are right, they must protect the information before launching it. Maybe with some trusted dedicated users who validate the information and add it to the blockchain. About the anonymity of the sources they had to learn to send something without being spotted (encryption pgp, Tor + VPN + not your connection + MAC adress change ... to avoid repeating things that happened with wikileaks) And only a small group of people see a single person can have access to the source that validates the information at first and the sending (no source included) to dedicated users who definitively validate the info. Or something like that, I did not really think about it.
But I think they had brainstormed about it and have much better ideas than mine.