Timeseries collections are going through a re-architecture in 9.0. Timeseries collections used to be backed by views, but now will have a single namespace without a view. SPM-4217 added support for all aggregation stages for viewless timeseries including $lookup, $unionWith, and $graphLookup. This ticket should be to add testing that cross-db $lookup, $unionWith, and $graphLookup work with the old and new timeseries architecture. 

Since the old architecture of timeseries depends on views, I marked this ticket as dependent on SERVER-110301.