Note this thread: http://www.flyertalk.com/forum/north...-upgrades.html

Not that many folks here are tripping over themselves to use miles for upgrading domestic NW/DL flights - but if you were planning on, for example, upgrading the NW/DL 744 or 330 to Honolulu to get the WBC seat without a copay, you will need to watch your fare classes.

Not sure if these changes have made their way to the CO system, or if this policy change affects the use of CO miles to upgrade NW/DL domestic flights.