Edward Snowden is not coming back to the United States. It is unlikely that many countries would agree to accept Snowden either. Therefore, Snowden should apply for Russian citizenship so that he can remain in the country the rest of his life. Russia has been kind to Snowden and its probably the best life he could have anywhere.
He probably would not receive a very warm welcome back home, so if becoming a Russian citizen can help him move on and be productive, it is not a bad idea. Hopefully, Snowden will choose to do something more positive than get caught up in espionage in his future endeavors.
Snowden doesn't have a lot of other options. The United States doesn't want him back and there are a lot of other countries that won't accept him. If he's safe in Russia that's probably where he should stay. Russia seems to be putting up with him so he should just finish out his life there.
Snowden is an American citizen, and should return to his country. Yes - this will mean that he will be imprisoned, as he should be. Snowden's revelations, because they were not carefully considered prior to being published, cost this country an immense amount of political capital, expense due to failed operations in flight, and even American lives.