I have no info about Delta, but wanted to join you in your determination to NIP while flying.
My DS is 22 month old, and we are at the age where mama-milk is the magic calming elixir of happy toddlerness. At the edge of a meltdown, mama-milk will turn the situation around.
So we will nurse on the plane, as I am sure the other passengers would prefer a happy (quiet) milk-loving dude to the ear-splitting seat-kicking demon he can become. I certainly do!