I've long doubted this as a serious problem. With the amount of packet filtering and what not that ISP's can manage on the fly, why can't they simply use a NAT

I've long doubted this as a serious problem. With the amount of packet filtering and what not that ISP's can manage on the fly, why can't they simply use a NAT to translate an IPv4 into an IPv6? It would fix the problem with most NAT's as both IPv4 and IPv6 can be tied together allowing a permanent IPv4 address to be a IPv6 on the net.