It would be amazing to be able to have empty shulker boxes stack. Would make inventory management much easier and not require so many chests and hoppers to store them.
The issue is NBT data. Even if it may appear as empty, the NBT data is sometimes different with something unseen causing it to not stack. Shulker boxes in general aren't meant to stack so why should empty be any different?
I know it can be done with carpet mod on the server and another mod like tweekaroo on the client side. Not sure if it's possible from just the server end. I know we don't have the NBT data on the client side, but wouldn't the server have the NBT data?
I'm sure it's possible. But meddling with base level vanilla mechanics isn't really something EMC does. There's a ton of datapack changes that would be super cool to have (like a lot of vanilla tweaks) but it gets difficult to implement on a large scale.