It was silly of Assange to wait through the tenure of a US government that was entirely disinterested in him until the current US president, who has a different attitude.
I wouldn't be so sure. In some matters, Trump is smart, and this might just be one of them. And Trump looks a lot less afraid of defying his robo-bureaurats (who would actually administrate an extradition and trial) than other presidents.
Trump, or a smart advisor, might have more interesting ideas. Like the fact that Oz itself is a close ally, and could probably find dirt on him within its own jurisdiction if it were so minded.