Ah yes, the completely logical argument that in order to be able to complete a rendition outside the legal process, those dastardly Swedes decided to commence a very public legal process against him requiring him to be on trial in Sweden...

(The UK makes dubious decisions to repatriate asylum seekers to countries like Egypt all the time FWIW)

That is a pretty logical argument. The Swedes have a legal system that is going to be quite different from the Anglophone common law systems and we can't really predict exactly what will happen. As monocasa linked, the Swedish legal system is not in a position to resist US demands backed by a threatening attitude. One incident is more than enough to establish that Sweden will likely fold if pressured.

It is reasonable to think that the Swedes have identified a different avenue that they can use to have Assange leave the country care of the US, and that they would exercise that option once they have him in custody.

That is almost certainly what Assange thinks. I don't know I've ever seen the likely penalty for what he was charged with, but I doubt it is more than a decade and he would have spent longer than that in the Ecuadorian Embassy the way things were shaping up. His actions are only rational if he is expecting the US to be involved.

... yes, Sweden's public historical willingness to cooperate extralegally with the US in ways that the UK is not is in fact pretty good evidence of... exactly that situation being capable of occurring.

You miss the point. If Sweden's true motivation lay in doing something outside the legal system, what on earth was the protracted legal process for unrelated allegations of offences committed in Sweden all about? And if Assange's true motivation was fear that the Swedes were unusually willing to act outside rather the legal process rather than within it, why was he so ambivalent about this threat that he chose to live there and stayed there until his lawyer received notification legal proceedings against him had reached the stage where he was due to be charged?

It's certainly amusing to see Assange fans rewrite history to make the UK the good guy when it comes to not cooperating with the US over extraordinary renditions (or indeed ordinary ones). Even the UK government wouldn't make that claim.