i really think no items should be consumed in PVP and the same would go for berries.
PVP should be more skill oriented than a farmfest
for example in the future the implementation of Weakness Policy ( not sure if it does currently exist in the game ) would run into the exact same issue
making it easier overall to predict the foe's moveset and it may also limit the usage of some 'low-rated'' pokemons in PVP