3rd party boxes like WDTV LIVE and Popcorn Hour are picking up steam. With wireless N, it should be possible to stream HD content to said boxes. These devices don't play DRM'd paid content, but they do play downloaded content from the net.
I imagine there's money to be made in set top boxes. Microsoft/PS3 rent movies/tv shows already, and netflix streams.
I suppose you don't really need to sell people boxes, you need to make a content or service available.