I read that Firestore can now query across subcollections. Is the firestoreConnect HOC from react-redux-firebase capable of utilizing this feature?
Collection Group Queries were released at Google I/O last week (May 7, 2019). A quick scan of the react-redux-firebase release notes shows no mention of them at this time, so it seems like they're not supported yet. You might want to file an issue/feature request for it and monitor said release notes for updates.