Without much fanfare NSX 4.0.0.1 released earlier this month. Among other features, there is IPv6 support. However, a big requirement is you must complete your N-VDS to VDS 7.x migration before upgrading to NSX 4.0 Oh yes, the NSX-T name is now retired (along with NSX-v), so NSX-T is now .. plain NSX.
Here's the release notes: https://docs.vmware.com/en/VMware-NSX/4.0/rn/vmware-nsx-4001-release-notes/index.html
The release notes include a link to this extremely detailed doc on N-VDS migration: https://kb.vmware.com/s/article/79872
