IPv6 deployment for hosting and developers

Talk on the implications of deploying IPv6 for hosting platforms and developers.

Rough notes

Why is IPv6 deployment so slow?
Adding AAAA records 'breaks' SSH (interactive and automatic deployments)
Mail over IPv6 without SPF and DKIM stops delivery to large mail providers (e.g. Google).
Apache VirtualHost *:80 includes v4 and v6, whereas nginx requires you to use listen 80 and listen [::]:80
If multiple protocols are available, which should be preferred? Linux seems to go for IPv6 first, but any which prefer IPv4 will never see the v6 service.
What is the benefit for hosting platform customers?
What is the incentive for incumbent providers?
IPv6 deployment can and does break things.
Benefits are vague and in future.
IPv6 is like PHP 7 - yes you should do it but there's limited immediate quantifiable benefit to the customer.
IPv4 works. The only problem is a lack of addresses, but you can hack around that, and it doesn't matter to incumbents.
Double the number of connectivity tests to run and services to monitor (assuming dual-stack).
Firewall solutions and edge routers might not support it - expensive to replace
Getting v6 addresses is a faff compared to v4
More customer co-operation required (c.f. ISP where you can often switch it on silently, especially if you manage their equipment or can push out updates)

RIPE 733: "The size of the allocation made will be exactly one /24.", "The sum of all allocations made to a single LIR by the RIPE NCC is limited to a maximum of 256 IPv4 addresses (a single /24). If this allocation limit has been reached or exceeded, an LIR cannot request an IPv4 allocation under this policy."
Who regulates RIPE et al? They have power to allocate a scarce and valuable resource.