The old Wild Mushroom spell for Balance Druid has been updated with new text in the last Dragonflight Beta build which could indicate that Mushrooms are returning as an ability for Balance Druids in Dragonflight. If this is implemented, it should allow them to do more damage on AoE!
New Mushroom Spells on Dragonflight Beta
Recently, Balance Druids received an update on some of the changes coming to the Dragonflight Beta.