There is a new serverStatus section, "catalogStats", which has the following schema:
"collections": number of user collections (non-system collections on databases other than 'config', 'admin', and 'local')
"capped": number of capped user collections
"views": number of user views
"timeseries:" number of user time-series collections
"internalCollections": number of system collections or collections on 'config', 'admin', or 'local' databases
"internalViews": number of views on 'config', 'admin', or 'local' databases