I've thought a lot about cryptographically verifiable timestamps as an alternative to and defense against patents, as I'm sure others have as well. I'm glad that you and others are looking at P2P solutions to this problem. The big challenge would be getting expert witnesses to testify in court that the timestamps are valid, or otherwise convincing the court to accept them.

The switch to first to file might render this moot, though, since it seems that inventions that are never made public can be "stolen" by someone else filing a patent at a later date (corrections welcome).