They're getting better at it, at least. They also recently added v6 support in their NLBs and you can get a /56 for every VPC for direct access. I don't think they offer BYO v6 yet, as they do for v4, but it will come.
Since we are deploying BYO IPv6 in AWS, I can assure you they do offer it now. That was a blocker for us.