I have not seen Assange asking any promise to Swede. Ecuador did, Assange I don't think so. I think you nailed it though on what kind of guarantee he could hope for. I think he knows very well that's impossible to juridically formulate the kind of protection it would want to have. Therefore yersterday he didn't even formulate such request he took a higher stance (and even more improbable to succeed) by asking the US of stopping the FBI investigation.
The article not only contradicts what you just said (about Assange making demands), but links to other articles considering exactly those demands in detail. You're incorrect: Assange himself asserted that one (of presumably many) condition of his acceding to extradition is an undertaking that he not be extradited from Sweden to the US.
