Nothing would be stopping ISPs from adding one or more non-ICANN DNS servers in their resolution chain. In fact, independent ISPs may do just that if they're no

Nothing would be stopping ISPs from adding one or more non-ICANN DNS servers in their resolution chain. In fact, independent ISPs may do just that if they're not explicitly banned and there are a set of standards standards in place. DNS is one of the easiest thing to do infrastructure-wise on the inter-networks.