Painting separate block faces and allowing small components to occupy the same block
Having the ability to paint one block face with a separate color/skin so the outside of a build is separate from the inside.
Allowing blocks with small collision meshes to occupy the same space as long as they don't overlap. This would allow light and button panels to be in the same space or a light and a catwalk.
I believe this tweet would help players create more compact builds and expand their creativity