Deciding whether under s91 of the Extradition Act, "the physical or mental condition of the person is such that it would be unjust or oppressive to extradite him", is a very fact-specific issue rather than a legal question though.

The appellate courts are generally there to resolve legal questions not factual ones—I'd question the Assange case, or other similar cases would raise a similar legal rather than factual question.

There has been a trend towards applying s91 cases for defendants with autism spectrum disorders: the courts didn't in Gary McKinnon's case, but the Home Secretary (Theresa May, before she became PM) justified her denial of the extradition order on that basis. In Lauri Love's case, the magistrates' court allowed the extradition order but it was overturned on appeal in the High Court on the basis of Love's not being able to cope in US custody with Asperger's syndrome. In the Assange case, the magistrates' court followed this established and rather persuasive precedent.