The under-resourced Canon USA technical services department has not yet returned my multiple calls in regards to questions about the latest Canon announcements, but MegaPixel.co.il
has published a worth-reading interview that answers some of the questions I have (thanks Niklas).
"The primary objective when designing the EF 24-70mm f/2.8L II USM was to deliver exceptional image quality and a compact design. While including optical IS was desirable, we felt adding the technology in this lens would have comprised these prime goals."
Read the full interview here