This has been a common suggestion since before the Publix Suffix List existed, as you can see from the linked issues in the text (and the references to the IETF

This has been a common suggestion since before the Publix Suffix List existed, as you can see from the linked issues in the text (and the references to the IETF DBOUND WG). Like most things, on first glance, it seems like it does make sense. Except it has a lot of issues, which you can see have been discussed for 15 years without resolution, even though yes, it would scale better.