if you care for my opinion, it's not limiting and it is already quite complex and challenging to manage 3 groups of retentions. Besides, I don't really see the point of creating more, especially considering that the log chain will be shared among the management groups or else you are marking your backups as PIT (point in time Restore) only, meaning you lose last changes after backup time.
however, you can always raise a Request for Enhancement (RFE) through the sales channel.
hope that helps,
Domenico.