Dan Larimeer (creator of Steem and EOS) said in an interview with Jeff Berwick that he was going to create some sort of blockchain arbitration system but I haven't heard anything else about it. I would think he would do something to keep track of who the best arbitrators (basically jurors) are. I agree with you about juries for civil cases. For criminal cases I'd always prefer a 12 man jury because the burden of proof is so high I would just want to take my chances creating doubt in a few. But for civil matters I agree. There's probably less sense of civic duty and the most dominant personality will take over the jury room. It would be great to implement something like a steemit reputation score.