I would absolutely agree with the idea of not being able to put them into the enderchest, only because of the fact that there IS ALREADY a way to save all your valuable items from enemys by SIMPLY LOCKING YOUR GODDAMN CHESTS. This isnt too complicated, is it? So theres no reason why shulker boxes should be placed in enderchests. Enderchests are a good thing to let every player keep 27 items / stacks of items 100% save and i honestly think thats already more than enough.

Also i dont support the idea of not adding them at all since there are already people who bought lots of shulker eggs, I have quite alot of shulker eggs myself, and i dont see how they are OP if they arent able to be put in an enderchest.

They just save space in your base if you have a ton of stuff and dont want to build huge vaults.