Its isnt just Blm who would need twerks.

-Summoner would be useless in a dungeon like Aurim Vale.
-Drk couldnt hold aggro on a pack of void mobs.
-Paladin wouldnt do better agains holy mobs.

-ppl would want to take 10 mins to gears up accordingly to the dungeon they got as roulette.
-24 men raids would be a "lunch break" at every floor.

The elemental changes would be minimal to not destroy a job and would take time to implement.
Its just not worth it.