With the advent of more hardware streaming devices ready to take advantage of Netflix's video streaming, the only setback for people would be video selection. If Netflix can beef that up, a streaming-only option that is somewhat discounted from their regular service rates would be very attractive. Netflix has found in their own studies that given a choice, many people prefer to use their “Watch Instantly” feature over waiting for a DVD. In fact, there's over a million Xbox users currently using that feature.
Netflix definitely has the subscriber base and the appeal to make such options viable. Their only setback is video selection, where their online library still pales in comparison to their massive DVD library.