If you look at the post you will see that multicast support has been there for over two years. However as Martin has said this is controlled and enabled via the NDI toolset and the correct setup of your network for Multi-cast. Not for the faint hearted unless you know how to configure your switches for this. The step by step instructions are not really possible because all switches and networks are different but you can find general documentation for this on the NDI.tv website. I would give you a direct link to the documentation but I am going to assume that you can use google and do your own research as you seem to be highly competent.

Well, if it's possible, I've never gotten it to work in any of my testing. You can enable multicast in NDI Tools on the machine vMix is running, but vMix Outputs aren't actually multicast. Other sources on the machine do multicast.

That being said, another possible solution for the OP. Run an instance of NDI Bridge set in local mode (use /LOCAL argument if you want to run it automatically from task scheduler or command line), and set to Do Not Transcode. Make sure NDI Access Manager is setup correctly for multicast on host and targets (and the network, of course), and you should be off and running in multicast mode (point clients to the Bridge stream of vMix Output instead of directly at vMix). You'd probably want to run NDI Discovery Server (in the SDK) on the same machine as Bridge as well, and point your clients and vMix machine to use Discovery Server (in Access Manager settings).

This helpful in broadcast studio applications, where there may be 20 monitors throughout the facility showing PGM feed, etc., but of course would work in your scenario as well.