Trump strikes me as far more likely to grant him a pardon than Biden. Biden is neoliberal, which are just as hawkish as neocons (they’re functionally identical). Trump is more of a populist, anti-war, “anti-deep-state” (i.e. intelligence agencies) sort, who has at least entertained the idea of a pardon.
Trump had 4 years to free Assange but did nothing. He will say anything to get elected. It's surprising how people don't see it. In Texas we call that 'All hat, no cattle.'