Consolidating sql databases
System databases will be stored on SSD storage that is local to the compute node where the database engine and SQL Server Agent are running.
There will be no artificial limitations on the throughput of the storage that is connected to a Managed Instance, it will be limited by the capabilities of the Azure Premium Storage platform on which it is built.
These are documented by Microsoft at High-performance Premium Storage and managed disks for VMs.
The storage in use by the Managed Instance ranges from P10 to the upper limits at P50.
Azure SQL Database Managed Instances are built on the Azure platform and are a tightly integrated Paa S offering that competes with the likes of RDS for SQL Server from Amazon.
However, there are key differences in the architecture that make Managed Instances a different proposition.