Sure, but there's not really much reason too (IPv6 still has private/non-routable addresses, so you might want to). NAT on IPv4 is used somewhat like a firewall - because there's nothing to configure - whereas with IPv6 the address space is large enough that there's (almost) no reason to use NAT (that I find convincing), and if a firewall is still desired, that can be run independability (for example, ip6tables).
Edit: To respond to your other comment, no, there's nothing stopping ISPs from inflicting NAT on IPv6 too, other than the consumer asking "why am I behind NAT when there is no shortage of addresses?".
Edit: To respond to your other comment, no, there's nothing stopping ISPs from inflicting NAT on IPv6 too, other than the consumer asking "why am I behind NAT when there is no shortage of addresses?".