If he were working for Russia, wouldn't it be more plausible to give them the secrets (just "forget" your USB stick in a cafe in Honolulu, which Ms. St. Petersburg sitting next to you will find...), and at the threat of discovery, go underground, and let himself be smuggled into Russia?

Why go to the trouble of trying to contact Greenwald, and Poitras. He tried to get Greenwald to set up mail encryption, it failed, Glenn ignored him for a few months until he managed to reach him through Poitras. A man who's sold state secrets and afraid the Men in Black are about to come would not wait that long.

But anyway, you deal in absolutes "There is absolutely zero reliable information on Snowden's motives.", so you probably know best.