In the context of SERVER-84243, achieving a clear separation between (1) routing information and (2) filtering metadata has proven to be extremely challenging, particularly when attempting to approach the work incrementally. The difficulty lies in implementing a step-by-step process that maintains clarity and structure throughout.
The goal of this ticket is to explore alternative solutions that can still achieve this separation while allowing for incremental and safe progress.

Regardless of the "Shards can act as routers" project, this work remains essential to ensuring that the shards are fully authoritative.