The way Directv is implementing 4K it will require two tuners per 4K channel (two transponders will be bonded to carry three 4K channels) They aren't doing that yet, but have designed things with that in mind. Thus you have the HS17 which has 16 tuners, subtract one for the SWM guide channel leaving 15, can only support 7 "tuners" when someday all of them are 4K capable. It could support more TVs now, but people would be pretty unhappy if it supported 11 TVs and then the next model 9 and the next model 7, so they have set the limit at 7 where the ultimate limit will be. Building it with expansion slots less than 1% of customers would use would be wasteful. If/when they decide to support customers with more than 7 TVs on the Genie 2 platform - which unless they change things is their future direction - will be through allowing more than per account. That would be FAR cheaper than making them expandable. And no matter how expandable they make them, it won't be enough for someone.