I've read (searched) the thread, but didn't see this addressed specifically ...
From :
https://www.delta.com/content/www/en...tificates.html
*Mileage Upgrades fare class restrictions that vary by region. Flight within the US 48 are eligible from Y, B, M, S, H, Q, K.
Mileage upgrades on international itineraries including Mexico, Caribbean, Bermuda and Hawaii are eligible on Y, B, M.
I'm reading that as Hawaii mileage upgrades now require M+, where as before it was K+.
(Amazingly, I was able to use miles to upgrade myself+partner on a K fare from ATL-HNL on the 330 on 12/30/12.)