Prediction: Mike Flynn will be star States Witness when Russiagate charges are filed against top administration officials (and perhaps against Trump himself).
Carter Page, Roger Stone and Paul Manafort have agreed to testify for the House Committee (not Senate), the house committee is run by Trump Loyalist, so these guys are sticking with the party line story. (The Senate committee would have real teeth, so they are staying away from there.)
Flynn is the only one to have registered as a 'foreign agent' sense the accusations were revealed. He is the only one who has not publicly spoken out, nor has he copped to the party line touted by Steve Bannon and Breitbart. His registration as an FA opened the door to immediate felony charges of espionage, they were not forth-coming. Why?
This smells like Flynn is working with FBI and needs to keep his mouth shut in exchange for an immunity deal when he finely testifies in open court. Mark my words. If the house does not subpoena Flynn in the next few days then he is working with the Feds.