Brian Thomas our commitment is to provide a secure and complaint boundary with all of the Microsoft 365 services and features coming to our Gov cloud environments. We'll focus on the most popular services first, and make sure that we audit and create the necessary controls needed to meet FedRamp and SOC requirements for controlled data. You can find our current offering list on the below sites:
Office 365 US Government Service Description: https://docs.microsoft.com/en-us/office365/servicedescriptions/office-365-platform-service-description/office-365-us-government/office-365-us-government
upcoming offerings on www.microsoft365.com/roadmap
sanyog gulaty the US Government offerings are setup to choose the environment meets that compliance and security requirements for the data that your handling. It would not be a good experience to put a single user on multiple tenants, and the individual services are aligned to one of the three environments (commercial, GCC, or GCC-High) for more information about the compliant boundaries please reference the service description above.