Working on my Stronghold rework idea and noticing that we have a full set of Mossy variants, but not a full set of Cracked variants. While that is an obvious suggestion, the more interesting idea would be if Cracked variants are also missing a piece of the block.
While it's weird that Cracked Stone Bricks are gained by smelting regular Stone Bricks, when they are used as a part of Strongholds, they are to show the age and wear of a derelict Stronghold. To further emphasize this, a missing piece missing from them would look very nice, and can have a few functions when it comes to compact designs (though this would ask such functionality in other variant types). The icon for the Cracked variants would show the missing piece, and all variants would be considered partial, and also probably best put in the decoration blocks creative section.
The player will be able to control where the block is missing the piece in whatever way is best and possible (let's leave that to Mojang to figure out). At best, I'd probably say that it would follow stair rules, the missing piece is on top when placed on top of a block or the bottom side of a block, and missing on the bottom if placed underneath or the top side of a block. The missing piece will tend towards the player, while being determined by what side of the block they place it on (e.g. if a player places it on the right side of the top side or the bottom-right corner on the side, the missing piece will be on the right). The blocks will effectively always look like an inner corner stairs.
Stairs are a bit tricky because they already have their own orientation rules, but best case missing one of the two lower stair pieces (upper stair pieces if upside-down). If a top stair piece is missing, it could cause outer corner stairs to become slabs, which you can just use a slab variant (a Cracked Slab will also allow a "second" missing piece). Same as above, which lower stair piece is missing is determined by placing it on the left or right side of the block accordingly. These will effectively look like outer corner stairs by themselves; inner corner stairs can look like sideways full stairs, and outer corner can look like... a tripod on its side?
Slabs are the same as the full blocks, missing a piece that is towards the player determined by the side in which it is placed on. However, a Double Slab will be missing a piece for each individual slab, and can be used as desired (can create a sideways stairs).
Walls are missing whichever piece as similar above. Normal placement causes the missing piece to be on top, and upside-down will make the missing piece be on the bottom. For functionality, a top half missing piece also removes the invisible hitbox above it, and a player can climb a wall with two adjacent missing pieces on the top. Poles will also be half-height if that section of the wall is missing, and can be climbable (allowing the player to jump onto the rest of the wall).