Maybe Sweden could give a legally enforceable guarantee not to extradite to the USA - or the USA could give a legally enforceable guarantee not to seek extradition.

We know that fair treatment for Assange in the USA will not happen. Look at the poor bastard who handed over all that US stuff.

Fair trial on the sex charges in Sweden seems unlikely too - and AFAIK what Assange is alleged to have done in Sweden is not an offence in the UK.