Update:

Confluence copy product data is now available for all customers as an Open Beta on Admin Hub. This is the recommended way to move confluence data across sites instead of importing confluence spaces or using the support led CLI. Read more for steps to follow to move Confluence data here: https://support.atlassian.com/organization-administration/docs/copy-confluence-data/

Summary

Customers that are doing acquisitions or would like to consolidate their cloud instances into a single cloud site, will require to perform a confluence cloud to cloud migration. 

Currently, the only option to perform a Confluence Cloud to Cloud migration/consolidation is to export and import individual space export and import, following this process import-a-confluence-cloud-space which is extensive work if there are big spaces that will need to be manually downloaded and uploaded or if there are a huge amount of spaces to be migrated.

Suggested Solution

Similar to the Confluence Cloud Migration Assistant, build a tool to automatically perform a Confluence Cloud space migration.

Workaround

An alternative is also to generate a full Confluence site backup and import this into a temporary server and use the existing Confluence Cloud Migration Assistant for server, but that will imply additional downtime for the total time to migrate and risks due to additional tasks involved.