Plex/Kodi are not afaik available on competitor boxes bt/virgin, and would think there would be significant hw/sw cost to ensure that on such an open system, drm was protected on the sky/bt/virgin media.
Consumers see netflix uhd now available on Bt (humax) box, so I would think sky cannot ignore that for long.
(presumably sky have negligible penetration on USA market where netflix is 'popular' using 40% network bandwidth @peak hours)