When it lands on a block it crushes it, stone becomes gravel, gravel becomes sand. Let them be pushed by pistons, the player has no problem carrying them around after all. Have a minimum needed fall height. This would make sand farmable, and just be a cool mechanic. It's very vanilla-themed and has lots more possibilities:
Dirt crushes into Clay?
Gravel crushes into Concrete if it's next to water?
Logs crush into Coal?
etc
As a builder the chiseled bookshelf has been really fun to use, however you either get a bookshelf or an empty shelf and so I think it would be cool if you could put potions, diamonds and emeralds, cobwebs, hearts of the sea, amethyst crystals, echo sharts, and other unique items that could be fun to display!
With this change also getting the block in all wood types would be cool because it would add even more decorative possibilities!
EDIT: I’d like to mention that it’s important that anything put on the shelf would have to stay pixel consistent with the 16x16 block so when you put items on the shelf they would scale to the shelves size!