If we're going to engage with the conspiracy theory angle (which I do think has some merit) then it's not about one single, definitive plan of action. It's actually about achieving a goal: stopping Assange from exposing secrets that various powerful people don't want exposed.
If you're willing to accept that the powerful do have secrets they don't want exposed then you should also be willing to accept that they probably don't care exactly HOW he's neutralized, just that he is. And judging by that criteria having him effectively locked up in the embassy is pretty good.
Hang on, hang on; is the conspiracy to get Assange to the USA, or to lock him up for a long time in Sweden?
From the sounds of things, I thought this was all a ruse so the US could grab him?