Same dashboard in GCP as Firestore in datastore mode. Collection storage space usage, index size, data size, etc.

Also, for multi tenancy apps in both modes (using subcollections or multiple databases or also schemas in native mode would be nice to have) an API that can tell how much resources - space, reads, writes, etc. did each customer use, to be able to offer some kind of pay-as-you-go type of subscription.