Hi, unfortunately it will not be possible as video requires a significant amount of bandwidth and I am fairy certain that the X8R/taranis system cannot handle video signals. I dont know the intricate details of A/V video systems design so cant comment but I think its safe to say its not possible. If anything it will be easier to integrate the R/C signals into an A/V signal, but since its an analogue signal distortions can cause a problem with the R/C signals which is why all R/C systems are digital now.
As for wifi, its possible to use that for long range FPV video with the correct long range wifi units and high gain antennas. Standard wifi equipment is designed for indoor use and not realy good to use directly on drones.
But otherwise it would be awesome to have FPV and R/C control integrated into one small unit so I like your thinking