In the case of a single enumerated plan, we use SingleSolutionPassthroughPlanner which doesn't know anything about the estimates for the plan.

It may be useful to display estimates in explain for this case. Otherwise users will have no way to examine estimate information without creating another index for the purpose of enumerating multiple plans. There may be internal uses cases as well when we hint indexes to evaluate the accuracy of our cost model.

Attached is a diff in progress for supporting this capability.

single-solution-costs.patch