Here's a note from Anne Labbe, a premier field engineer in Charlotte who's been looking into managed service accounts..

After painstaking research and tracking this down to the product team this is what I found:

1. Managed Service Accounts (MSA) are different from Group Managed Service Accounts (gMSA).  The reason I’m calling this out is because a number of the references floated around are for gMSA and not MSA.  

2. gMSA are not yet available, are not yet supported for SQL Server.  gMSA exist and are available and supported in Windows Server 2012 and higher.  SQL does not support them , but from an OS perspective, they exist and are supported.    

3. MSA are supported from Windows 2008 on for specific applications and for specific purposes.

4. MSA are supported from SQL 2012 on for use running SQL service accounts (all SQL Services) where they are confined to a SINGLE machine.  This means that this account can NOT be used across multiple machines.

The confusion came (for me at least) because the installation code was changed to check for the use of MSA. Since the code was not in the setup for SQL 2008, I was able to install an instance using a MSA. The product team has reiterated that although I could do this it is NOT supported and has NOT BEEN TESTED.

- Anne