if there would be a vMix app using SRT for for the video transfer but having the same features and ease of use as vmixcall, i think many users would be willing to extra for the app or an extra license to use it.

Larix broadcaster works great but is missing all the features of the return video and audio, which make vmixcall so great to use.
But more reliable connections and better audio quality are important in many cases. Specially when using vmix in a broadcast environment.

The flexibility and ease of use got vMix a big boost in the broadcast market in the last months. Better quality and reliability would make sure it stays there.