Oh boy. And containers were supposed to make things easier.
https://www.zerotier.com/community/topic/67/zerotier-6plane-...
Full disclosure: this is ours.
Currently Amazon, Google, and Azure have no native IPv6 support.
Also many are allergic to the security implications. You have to be rigorous with ip6tables and making sure everything speaks SSL or another encrypted protocol using authentication in both directions. Many things do not support SSL or don't support bidirectional auth.
Personally I doubt overlay networks are going away. Most backplane software like databases, distributed caches and event servers, etc. offers literally no security because it's all built with the assumption that it will run on a secure backplane. I have personally railed against this for years but I've found that it's a total waste of breath.
Even my residential cable provider gives me a /60. Anything less seems absurd.
The bigger issue is the need for a secure backplane, which will remain until all server software authenticates all sockets in a strong way.
I'm surprised that the bar isn't set a bit higher inside the cloud provider infrastructure for tenant separation at the network level. I suppose it boils down to the lack of assurance at an even lower level (who trusts Xen these days?) that seems unlikely to be fixed in the short term.