1. He pushed US media (WaPo) to publish by going to UK media (TheGuardian).
2. He released with reservation and regard to security, not all docs were published.
3. He voluntarily disclosed his identity for protection...if the public knows him, it'll be awkward, if he just disappeared.
4. [my opinon] He went to Hong Kong (specifically HK, not China), because it is still somewhat it's own country, yet a formidable adversary to the US through China's protection. Also, it's unbeknownst to us, if he released more information while in HK.
5. Russia recently had captured a CIA agent (although I thought it more comical then serious), and no extradition to the US. Again, another formidable adversary to the US, and it may have been a red flag for an intel agent to go to Russia.
By formidable, I imply that the US will not send a seal team in to these territories that have the military capability to strike back (I won't say the name - but Pakistan is what I'm implying here).