I'll tell you when the 6G iPod is coming out: September or October. Not sooner, not later.
Seriously, why did anyone think it would come out any sooner. Regardless of iPhone, Apple would want this product to fresh for Christmas, not Memorial Day.
I think it's the first option you mentioned ("...time to move on").
As for Rubinstein, that isn't new news. Apple announced that Rubinstein was retiring back in October. See here.
As for Avie, I do believe that came out of the blue.
She's also been taken off of the Executive Profiles webpage.
**Interesting note: Jon Ive has been promoted, he's now Senior Vice President. Not to mention the fact that he's now on the page (before he was just a VP and not on the page at all).