But once IPv6 only web sites starts to show up I don't think a router can save you as the browser would get a IPv6 address when doing the DNS lookup.
It's easy enough to NAT and rewrite IPv4 to IPv6 in the router. Intercepting DNS traffic for NAT'ing purposes is easy and "cheap" - I don't think any routers produced today would have any problem handling the extra cost in processing of that kind of rewriting.
If I was running a major ISP today, I'd be looking for routers with capability to bridge IPv4 via NAT to IPv6 transparently to deploy to customers so that I could start transitioning my backbone to IPv6 on my own schedule rather than be dependent on customer equipment.
