I would like the ability to force a framerate (25 or 50) from the callers camera if supported (like in obs.ninja ?). In obs.ninja you could add &fps=25 on the guest link. So if the callers camera supports 25 fps it will be set up.

The vMix Support answers:

„…the frame rate is fixed at 30fps for callers using a browser with vMix Call and this can't be changed at this time.
However if the caller was using vMix to call in (such as via the Trial or the Basic HD edition) then it will send either 25fps or 30fps depending on what frame rate they have configured in vMix.“

Thanks
Hannes