Does RelMdDistribution exist or as theory? Definitely inclined to "Exchange" over "Shuffle" as more generic/consistent with Volcano.
Note, looking at Ashutosh I wonder a little about the need to have range versus hash at the field information level. I'm sure we can come up with a use case but it seems to overcomplicate. We already have space exploration problems when trying to do distribution subsumption for joins with trait propagation so I would be cautious about adding more dimensions to that attribute.
