As an outsider, I don't expect the American government to ever pardon people like him. Presidents come and go but they all play nicely with the military powers that remain after their terms. When presidents promise to do things the rest it the government doesn't like, those promises only get broken. Trump didn't complete his wall, Obama didn't close Guantanamo Bay, and so on. Presidents aren't kings, their actions will follow them and have consequences even after leaving office.
Biden might pardon Snowden at the end of his term, but don't count on it. I haven't seen a single sign that Biden (or any American presidential candidate for that matter) would side with anyone for leaking government secrets. The government is sitting on many more juicy details that'd upset the global political balance and transparency is not in the USA's interests.