Make the "puff" animation the redstone cloud dust and color it based on the potion effect. Have a shift right click function to return the items to the player. Have it drop its contents when broken, like it should. Make the number of grinds configurable. Add a sound effect and swing animation to the pestle usage to make it more interactive.

Most of these have been done, actually, with the exception of the right click function, and it's a good idea, so I'm holding off closing this one. Also I probably forgot to make it drop its contents when broken, so those two need to happen.