I think in practice, the first time someone needed to do this, a bunch of high grade academic cryptographers would acts as expert witnesses pro-bono. From there, it would be like a hacking case - an expert explains the issue to the jury, who take a decision. Assuming it is technically sound, bitchain certification would win.

Subsequent cases would be able to use the precedent, and win with less interesting experts.

These comments are actually making me think of this case:

http://en.wikipedia.org/wiki/Howland_will_forgery_trial

I've faced these authentication issues in Asia and the Middle East. There is an increasing willingness of authorities to trust non-traditional means of authentication through neutral third parties. For example, I recent pointed to a commercial corporate records provider as a source of authentication of a foreign corporation being in good standing and the local Middle Eastern authority was willing to go online, look for themselves and conclude that the information was correct. I beleive that such forward-thinking authorities will begin to participate in BTC hashing and be willing to gather the information for themselves.

If you think about it, this is a lot more convincing than getting a ribbon-covered document from a foreign jurisdiction that you may not be able to read, even if it authenticated by a series of trusted authorities (a chain of embassies in this case).

Bitcoin might let you say things like "both parties signed this document on this date" but you will still need a jury to decide "Action [foo] does or does not constitute a violation of this document which they both signed on this date".