DJB's (sketch of a) solution seems more like 6to4, where every IPv4 address automatically gets a /48 IPv6 prefix. It was deprecated due to unpredictable reliability.

It doesn't make sense to have NAT64 on every router, because NAT64 is stateful and needs to be properly engineered into a network. There are also alternatives like DS-Lite and MAP, with different design tradeoffs.