I believe there is a way to get rid of explicit leaves without loosing the simplicity of the balancing operations.

[make-github-pseudonymous-again]

This involves only creating the leaves whose parent pointer is accessed and hard-coding the black color of implicit null leaves in the code somehow. This should be possible because the former is only required at the beginning of a deletion balancing operation, and the latter can be done by breaking symmetry, which is already done to some extent.

[make-github-pseudonymous-again]

This would save a lot of space since a tree with n internal nodes (Node) has n+1 leaves (Leaf). Each Node is five pointers, each Leaf is two pointers, could be reduced to one pointer by hard-coding the color, but even then that is at least a sixth of the total space resources.