This reminds me of the sentencing of the "January 6 insurrection" guilty pleas. As I (a non-lawyer) understand it...
Regardless of whether you consider it an insurrection or a protest march petitioning the government for redress of grievances...
In the wake of the events, the fed busted a bunch of the participants and left them rotting in prison for months (over a year), with no end in sight. In many cases this left families with no breadwinner, enormous legal costs, and expectations of losing all their property as part of some eventual conviction.
Then the prosecutors offered some of the defendants a plea deal; Plead guilty to a misdemeanor or short-sentence felony and we'll drop any other charges.
Rule of thumb: a misdemeanor generally is a crime with a max sentence of no more than a year in prison, a felony more than a year - which is why you see "year and a day" max sentences on some crimes. An accused person already in prison for over the max sentence would expect that accepting the deal would result in immediate release with "credit for time served" (and others near the max might expect release much sooner). So some of them went for it.
Came the sentencing some judges applied a two-year sentence enhancements for "substantial interference with the 'administration of justice.'" OOPS! No release for you.
I'd expect them to pull the same sort of thing on Assange if he were foolish enough to plead guilty to anything, no matter how minor.
(By the way: This particular form of the practice, as used on the Jan6 participants, was just recently struck down. But the decision was based on Congress' certification of the presidential election not qualifying as "administration of justice.'" So this wouldn't apply to whatever enhancement trick they might pull on Julian.