Experience with IPv6-only servers

We have been so ~~greedy~~lucky to have a big enough public IPv4 network allocated that we have not required any private subnets on our servers. However we are about to run out of public IPv4 space in the near future. A quick look at our firewall reveals that about half of the servers don't need a public IP address and are only reached by other servers, clients or through VPN. This is things like database servers, storage arrays, authentication, recursive DNS, VM clusters, etc.

Had it been two years ago I would have set up a private IPv4 subnet and set up NAT and play with routing tables and firewall rules to get the servers to use that. However we have been running dual stack for a while now, and so have everyone else. Is it maybe time to switch off IPv4 on servers or is it still too early. If it is too early then we can always setup NAT64 to get the remaining IPv4 only services.

I started playing around with a VM and soon discovered that we were less dual stack then I though. If an IPv6 service fails it will quickly fallback to IPv4 so you may not notice that things is not setup correctly. Most of the issues were configuration though and remembering to setup "listen" statements and "allow" statements for IPv6 in configuration files. There were also some servers which had no ip6tables configured and were blocking everything. We are now running a full test environment with several physical computers and lots of virtual computers everything setup without any IPv4 access. There have been some minor issues with application which support IPv6 but require an IPv4 address to be configured or require special arguments to work with IPv6 at all.

I am really surprised at how many public services out there supports IPv6 and it is possible to read your mail, search the Internet or browse wikipedia without any working IPv4 connection (no reddit though). More importantly most of the software repositories, NTP servers, DNS servers, etc. all support IPv6 so it is actually possible to run in this configuration.

Before I try this out in production I would like to ask if anyone else have experience running a server without IPv4 and if there may be some pitfalls which I have not seen. As of yet I am a bit worried that it all looks to easy.