Don't know why, but the turtle farm seems to be broke. Hung out in there for 2 hours last night, got less than 60 turtle parts (I need about 1000). This morning, two!
I'm gonna vote for a new recipe for shulker boxes, considering their extraordinary usefulness.
Chests and emeralds, perhaps? Still have to work for it, but there is pretty much no other use for emeralds.