That's essentially what the Sega Channel adapter was. The service didn't rely on something like you'd expect from a modern cable modem. The games were broadcast in a round-robin fashion (presumably broken up into blocks, as I remember the time to initiate a download was never super long, but the whole process to play a game did take a small amount of time). The adapter thus needed hardware and software in order to decode with the one-way signal to download the menu and game data.