The new GUC terms seem to say that you *can* upgrade from A to business.
https://www.delta.com/us/en/skymiles...llion-upgrades
at the bottom click to expand "CURRENT GLOBAL UPGRADE TERMS & CONDITIONS"
section 7, Applicable Fare Classes:
"For travel on
Air France-operated flights marketed by Air France and booked in Y, B, M, K, H, L, Q, T, N, R, or V class, customers can upgrade into A class (Premium Economy),
or they can upgrade from W, S, or A class into Z class (Business Class). For
Air France-operated flights marketed by KLM, customers with a published fare booked in Y, B, M, K, H, L, Q, T, N, R, or V class can upgrade into A class (Premium Economy),
or they can upgrade from W, S, or A class into Z class (Business Class). For
Air France-operated flights marketed by Delta, customers with a published fare booked in Y, B, M, H, Q, K, L, U, T, X or V class can upgrade into A class (Premium Economy),
or they can upgrade from W, S, or A class into Z class (Business Class). In addition, customers traveling on an
Air France-operated, Delta-marketed flight and booked in P, A, or G class can upgrade to Z class (Business Class)."