I would pay for the app if it would encode and send a stream though, just so We could see just how taxing it is and within the capabilities of todays mobile devices.
A estimated guess based on PC performance info posted makes me think a dual-core arm64 1ghz+ should be able to encode 30fps of 720p using about 40% of it's cores. Seems low enough to be usable, on a mobile phone 480p would be more than adequate. Whoever finally makes a h265 bidirectional streaming video conferencing app first will likely have ppl flocking to it over FaceTime if they regularly use it over 3g/LTE...