I'll also note that the prosecutor was contradicted by Swedish legal experts already back when Assange was detained in the UK and Ny first made that claim. It was noteworthy also because Swedish police sent people to interview two suspected murderers elsewhere in Europe while Assange's extradiction case was happening, yet Ny continued to claim it was impossible for her to do so with Assange.
I think Assange was being paranoid, but I also think Ny was letting her own preferences take precedence over pursuing the case as best possible, for whatever her reasons might be (I've in the past suggested that rather than US involvement it's more likely she "just" wanted to make an example of him, but that's pure speculation)
EDIT: Here's a brief news item claiming the above assassin was indicted in absentia: https://www.abc.net.au/news/2003-09-17/man-detained-over-kil...
Here is a more substantial one: https://www.irishtimes.com/news/swedish-police-issue-arrest-...
With regards to the policy change, to some extent I dont care if they apply it consistently to other people now as well. Just that they changed the policy when they were chasing a guy who had pissed of and embarrassed the most powerful nation in the world seems very, well, convenient.
Perhaps more importantly, I'm not sure I am convinced that there has been such a massive policy shift as such. I would like to hear more about these other people that are being chased all around Europe by the Swedish prosecutor authority, but we don't hear about because they are not globally infamous.
I should perhaps add that just because Assange is (possibly) treated differently, this does not prove that there is some conspiracy against him or whatever. This case has gathered a lot of media attention and whatnot. In many ways a conspiracy seems unlikely, or at least unnecessary. Many of the actors involved seems to just follow the path of least resistance and/or acting in their own interest. Sweden does not have much to lose by doing this, certainly relations between US and Sweden are not damaged by this. Marianne Ny seems like a somewhat crazy feminist who IIRC has made statements that the methods she has developed for investigating crimes against women has "good effect on the perpetrator even in those cases where he is not found guilty by a court of law".
That article pretty clearly states that the prosecutor believed that Swedish law prevented the investigation from proceeding, and that matches what the prosecutor in the article you cited said to the tabloid.
The policy was changed because of Assange. It's not specially applied to him--the new policy applies to everyone. He's just the only one you here about outside Sweden because he's globally infamous.