ELBs (Elastic Load Balancer) supported IPv6 termination since 2011.
You'll need something it you want to download files from Github, because for some stupid reason they still don't provide IPv6 services for cloning and such.
It looks to be available, but (from the bottom of the article) "Regular NAT gateway charges may apply."
Yes the problem is NAT gateways are expensive, not free. AWS could easily run a "central" 6 to 4 in each region (not in your VPC), which the incremental cost of using would be near 0. Then you could use pure v6 (no IP charges). And actually be able to talk to things like github, stripe, apple, etc.