Technically speaking, it's doable. Just yesterday I've managed to send a NDI feed into a VPN tunnel to a colleague of mine in another city. For the sake of precision, the NDI feed was originated by OBS Studio on my machine, and received in NDI Studio Monitor on the remote machine.

Latency is good (definetely less than 1 second). However, quality is the issue. In order to avoid stuttering you have to decrease resolution and frame rate. That was totally expected. Fact is, NDI can be used effectively in a local network environment with excellent routing and cabling infrastructure.

As you may be aware of, there's a version of NDI, called NDI|HX (HX stands for High Efficiency) that indroduces a higher compression (h.264) and latency, reducing the data rate and making the signal more reliable over long distance transmission.

As far as I know, at the moment there aren't free software NDI|HX encoder/transmitters. However, there are at least a couple commercial solutions to achieve this result. Moreover, there are several SDI/HDMI to NDI|HX converters, and several PTZ cameras with NDI|HX output.

Extremely fascinating scenarios await in the future, in my opinion.