Well you have the option to stream on hitbox in 4k with the needed bitrate already (H264), or you can wait (2-4 years) till quicksync can encode AV1 and youtube does allow it for streaming. It seems twitch is not interested in quality, only in how many viewers they can serve as cheap as possible, so i think they will going the way of myspace before 4k streaming goes mainstream. (3500 kbit/s enforcement)
H265 has no future for streaming non DRM protected stuff