User Defined / Custom Mesh Map Input
Custom workflows that require access to custom, static mesh-map like maps would benefit greatly from this addition.
For example, if a static lightmap must be accessible anywhere in a texture set's scope, it must be computed at the bottom of the stack (assuming it's an SBSAR generator), and then much care and attention must be employed by the artist to manage scope and access to that data (usually requiring anchor points, which unfortunately adds a texture set relative dependency, which also affects Smart Material effectiveness).
In short, multiple instances or references to an SBSAR generator or bitmap can be avoided with a Custom Static Mesh Map. This also ensures that users don't have to worry about scope management as it relates to folders, since Mesh Maps are globally accessible in the layer stack.