> For my design, I decided to enforce that both key and value types are comparable, so I could build a simple demo using two hashtables as an index and reverse index with flipped key/value types.

Surely the demo works equally well without this extra constraint? If the demo had a generic function for creating a reversible mapping it would have been necessary, but as it stands, this extra constraint comes across as avoiding having to write the less aesthetically pleasing

  type Table(type K comparable, V interface{}) struct {
    ...