There is a new view for tags under inventory on NSX-T 3.0 that is an improvement. Are your needs regarding tagging related to the UI or API?
In Policy API you can see all VMs with a certain tag using a GET https://nsxapp-01a.corp.local/policy/api/v1/infra/tags/effective-resources?tag=test123
I tried this and it returns all VMs that have the tag test123.
You can also list all tag with a GET https://nsxapp-01a.corp.local/policy/api/v1/infra/tags/
If you give some more details on what you are trying to achieve we may be able to help.
Thanks for sending that over. I don't believe that API call existed in 2.5. I had to pull the details for all of the VMs and extract the assigned tags to determine what VMs had a specific tag. This is much better!