As you say, Alan, the American authorities now own all that blackmail info directly (if they didn't have most of it before).
As Assange's one-time American lawyer Weiner said a couple of years ago, (paraphrased) "The Americans want the photo-op of a manacled Assange being brought off a flight into the US". Journalist Stephania Maurizi explained at her Bergen talk last week that the reason they're so keen on that photo-op is that ... it will work as a domestic deterrent ('encouragez les autres') to warn off four to five-million American security agency staff who have security clearance - and who could potentially turn into hundreds of "Mannings" and "Snowdens".