Managed Instance is now offered as low as 4 vCore standalone deployment option. For deploying multiple Managed Instances, consider using Instance Pools https://aka.ms/mi-instancepools which allow as small as 2 vCore Managed Instance.
An error occurred while saving the commentJordi Meijer commented
We are running into this similar issue. We have over 2000 SQL databases and we're hoping this limit of 100 databases can be increased.