When holding an item in hand and looking at a block that's less than 4 blocks away, there should be a preview for that block.
It should have an opacity between 50 and 75% and should allow the player to see the height and rotation of the block.
The preview should only be visible for the player holding the item (for now).
This feature should be opt-in via config.

This is an idea for now.
May not be possible to implement (cleanly).