Why don't Sky simply update the firmware on their decoders, so they can be plugged directly into a fibre ONT? So you wouldn't need a dish, Or even an internet account. As Sky could pay Chorus directly for the fibre connection. Then Sky won't have any restrictions on how many channels they can offer, how many in HD ect.
At the moment an overseas pay TV company could easily setup in NZ. With their decoders running directly off fibre connections. Could get interesting if Sky suddenly found themselves having to compete against Comcast or another US cable company. Of course content rights would probably be the main restriction.