You've all got it wrong.
Yes, both the UK and Sweden have the temporary loan agreement, but Britain is first obliged to apply any extradition against whatever is currently outstanding - i.e. the request from Sweden in conjunction with the Interpol Arrest warrant, still in force. Had that warrant not been issued and had the USA issued an arrest warrant of its own against Assange (which it has not been unable to because the Grand Jury is still deliberating the charges) then Britain could then consider agreeing to extradition (not a temporary loan in those circumstances) to the USA. The Swedish situation is different: once the current extradition (from UK to Sweden) is dealt with then the Swedes would be in the clear to loan Assange to the USA at any point in time. Ironically, it actually suits the US that everything is delayed (while the Wikileaks Grand Jury deliberates). and, so, it would appear that moving to a country where there is no extradition agreement with the USA, the UK, Australia or Sweden may indeed be M. Assange's only option left (although a change of Government at some stage in Ecuador could then mean another move.)
Meanwhile, there are a growing number of articles in the press about the two complainants in Sweden and whether or not they (assuming charges are raised at some stage) will have their case heard in court. Unless Snr. Garzon can extract a guarantee of no onward extradition from Sweden or the UK (which it can insist on as part of the extradition) or even a guarantee of no prosecution from the USA, then a hearing in Sweden looks increasingly unlikely.