So a slim 360 Arcade for $149 and a slim 360 w/ some HDD for $199.
That makes sense and would be a good buy.
They definitely won't switch to no skus with HDDs. That would be silly, plus even in a slim size, they could still put a HDD on in a slightly different orientation. Plus, the slim model may still be the same width, just shrunk in the other two dimensions.
E3 is heating up to be really exciting this year.