In the degenerate case, any individual that ever registered a domain for another individual is a registrar. Arguably, evry ISP on the planet already is.
Registries are a necessity.
They provide a unique and mandatory technical function. It's similar to a car dealership that may license the car for a purchaser as a matter of convenience, but, anybody can go to the license office and register it themselves. It's unclear how the initial board will be selected. It appears the board is made up of people appointed by the SO's. But, the SO's are selected by the board, so there is an apparent bootstrapping problem here.