Julian Assange to testify before Congress?

Well certainly not in person unless there is an immunity deal.

Assange is to the internet what Luther was to the printing press. These are folks who grasp the implications of spreading the light and are willing to risk some serious privation to do it. Not many of those folks in history.

If congress wants to know the role Assange played in the 2016 US election, a few minutes on YouTube should give plenty information of his position on this question. (It's not like no one has thought to ask him about this before.)