Some time ago, it was reported that amateurs were to carry out some tests on 10m and 6m with reduced bandwidth ATV. I have no idea if these tests were carried out.
I think in the 1950s UK broadcast TV was copied in South Africa and Australia when the MUF reached band 1.
ATV is one area of our hobby I have never tried. These narrowband digital tests sound fascinating. I am sure that they will be well published when successful.