Relatedly - we have the same question asked recently by an anonymous volunteer on our public talkpage https://meta.wikimedia.org/wiki/Talk:Wikimedia_Enterprise#IPv6?

Thanks for reaching out @taavi!
IPv6 support on the Enterprise API public domains was not omitted due to a technical oversight. Rather, at the time the service was designed and launched, there were no explicit requirements for IPv6 from Enterprise users, nor any requests indicating a business need for it.
Supporting IPv6 would involve non-trivial engineering and operational effort across our infrastructure. Given the lack of user demand and the associated complexity, we prioritized other features that delivered more immediate value.
That said, we continuously reassess priorities based on user needs, and IPv6 support can be reconsidered if there is sufficient demand. Please remain subscribed to this ticket which we will file in our workboard to monitor any future updates.