The reason why Assange stayed in the Ecuador embassy for all those years was because he was afraid of, and had every reason to believe England would extradite Assange to the US. As long as Assange remains charged in the US, I do not see any way he will not be extradited to the US based on the treaty between the two countries.

After the 2020 election, Trump should pardon Assange. Assange has embarrassed many powerful people in DC, and Trump will not have political support for doing this. Depending on his margin of victory, and the state of Congress after the 2020 election, Trump may need to wait until after the 2024 election.