V, X, and a handful of other classes are "new" per the previous link. On the food chain, X and V are higher than E but lower than T. As far as I can tell, X and V are full-value* fare classes and are not brain-dead like E.
2013 - Fare Class Alignment Implementation
Nearly two years ago, Delta, Air France and KLM embarked on a strategic initiative to align fare classes for published and private fares. Delta Air Lines is pleased to announce the final steps of fare class alignment are about to take place.
Fare Class Alignment will be rolled out in four phases between January and March 2013. Once complete, Delta’s fare classes will be better aligned with its trans-Atlantic joint venture partners Air France and KLM.