For example, searching around, it looks like the US has asked spies to be extradited before and succeeded: https://www.nytimes.com/2018/10/10/us/politics/china-spy-esp...
I'm still not sympathetic even if he has a political defence, however. Wikileaks has published at least one classified UK document, which means he can be charged under the OSA in the UK anyway under the onwards disclosure clause (I don't know if they'll do this. Probably not, I would guess, due to lack of evidence. I do know there is a consultation ongoing to revamp the OSA partially in response to Snowden: press: https://www.bbc.com/news/uk-politics-57998950, law commission review: https://www.lawcom.gov.uk/project/protection-of-official-dat... consultation: https://assets.publishing.service.gov.uk/government/uploads/...). I think he would have stood a better chance of avoiding extradition pretty much anywhere else than the UK, including Sweden, which is why I am not sympathetic (if you're going to spit in the eye of the US, the UK is probably not one of the places to be when you do it). I'm also... perplexed, to put it charitably, as to why he'd avoid the Swedish extradition, as I think he would have had a better chance of avoiding extradition from Sweden to the US than the fight he currently has (where he has pretty much zero chance).