I think what he's pushing for is the ability to present any defense that he likes. Under certain statutes, you cannot raise a public interest defense. I believe the Espionage Act is one such statute. You cannot present a defense that is irrelevant to the commission of the crime, and under the Espionage Act it is the release of the information, regardless of intent, that is the crime. See here: http://dissenter.firedoglake.com/2013/08/09/obama-falsely-su...

Venue shopping would obviously help him (ie Silicon Valley vs Arlington, Virginia). However, I think what he's pushing for is to be able to raise the illegality of the programs the government was hiding from the public (and lying about before Congress). It is not at all clear that this type of evidence would be allowed, and is pretty important for how a jury would construe his actions.

You can't guarantee impartial, but you can, with the right lawyers, get a less partial jury. However, I think what Snowden actually needs in this case is jury nullification, and that would require some venue shopping he is unlikely to succeed at