When designing builds I find the Rod of the Shifting Crust extremely useful for palette swapping, except for one thing: blockstates aren't maintained. As an example, if I replace a stair that is facing north with another stair block, it will copy the direction from the stairs used to configure the Rod with, rather than mimicking the direction of the stairs it's replacing. If instead the Rod mimicked the blockstate of the block being replaced, it would make it so much easier to quickly try different palettes in a build.
The main blocks this would be useful with would be slabs, stairs, fences/walls/gates, logs (or anything that has a primary axis), doors/trapdoors, and waterlogged blocks. Any modded blocks with directional properties would also benefit.
For anyone familiar with WorldEdit, this is basically the sort of thing I want it to do:
//replace oak_stairs ^spruce_stairs
Some people may find the Rod's current behaviour more useful for certain tasks (e.g. if you wanted to replace a lot of bottom slabs with top slabs), so having the possibility to toggle between modes might be a good way to implement it.
Keen to hear others' thoughts ^-^