Depends on the Classic team truly, do they consider: a Warrior being the only Main Tank for raids, Paladins/Ferals/ShadowPriests/Enh Shams to be side-lined and excluded from dealing damage compared to Rogues/Mages/Warriors, and classes who had healer trees to be cornered into healing raids - all to be successful or a failure in design. And the bigger question being regardless of if it's considered a failure, would they take the opportunity to fix it or not?
As I've said, we've already heard from the Vanilla WoW Class Designer himself that certain classes didn't live up to the fantasy they imagined for them during Vanilla, that to me sounds like a failure in design, otherwise he would've said "class imbalance was meant to be the way it was in Vanilla, DPS Paladins should've been healing" or something to that effort.
Truly I have no issue whatever the decision turns out to be, I will enjoy Vanilla for the experience itself. It's just the most interesting topic I'm wanting to see the answer on at Blizzcon.