Would it be possible to add shulker boxes?
I've tried adding them manually (in-game as well as editing the block_store.json), but it didn't work out.
I tend to put them down and then forget to take them with me again, so this would help me locate them better.

Maybe other entity kind of blocks as well? (like chests, beds, item frames, boats, carts, dropped items, falling blocks, TNT)