My two IPv6 issues (even having had a HE tunnel in the past):

- My local ISP (US Internet, soon to be part of T-Mobile Fiber) hasn't enabled it, even though the CEO has said on Reddit for years that it's a priority. Now that they've been acquired who knows if it'll ever happen.

- Linode allows transferring v4 addresses between machines, so if I need to rebuild something I can do so without involving my client who usually has control over DNS. They do not support moving v6 addresses, which means that the only sites I have control over that support v6 are the ones that I control DNS.

Making IPv6 a thing seems like it would be super easy if a couple hours could be spent solving a bunch of dumb lazy problems.