The sling part would just take place of the actual cable channels (insert live tv service of your choice here as well, hulu/youtube etc), there are no cable providers here whatsoever this box is just a way to bring together cord cutter services in a concise way that anyone that is used to cable TV could get on board with, smooth transition.
People are willing to pay large up front fees if they can get rid of monthly ones, this box could be 200 dollars+ and it would sell like no ones business. People like the cable box experience, they dont like the high monthly fees.