A problem with that approach is that using satellites for streaming essentially means that a 2-way communication system has to be established so the "server" knows what you want to watch. The satellite TV system, as currently configured, is a one-way communication system. No information is returned from the satellite receiver to the transmitting satellite or ground station. Satellite internet systems, such as those provided by Hughesnet, require a much larger "ground station" with the capability of transmitting a signal back to the satellite in geosynchronous orbit.
It would, in theory, be possible to create a hybrid system which involved the use of a one-way satellite downlink along with the use of a separate uplink using, for example, the cellular network. At one time there were Hughesnet options that sort of worked in that manner.
Personally, I'm not convinced that's the way AT&T will go. As currently designed the satellite broadcast system can provide HD or even 4k signals to millions of subscribers because there is no "feedback" and all customers simply select from a fixed "menu" of channels. If, however, each customer is allowed to specify his own information content the bandwidth will be nowhere near adequate to satisfy the same number of subscribers.