Problem Statement/Rationale

Sharded collections can not be used in aggregation pipelines lookups nor can they be sent into the aggregation pipelines from exterior similar to scope, or at least we don't know how to do that... 

Steps to Reproduce

Tried and failed to migrate an existing incremental map / reduce job to aggregation pipeline. The job has a lot of scoped variables and prior lookups that it has to do and they are lookups in heavily sharded collections.

Expected Results

If aggregation pipeline is pushed as the only alternative people should use then it would be good if it is possible to do the same things with it.

Actual Results

Doesn't work