I don't think movies will follow the same route as music and become a (completely) non-tangible format. The reason for this is that the movie companies would not have control. With a disc, there is some form of copy control. This is not the case with MP3's. I know we can go to iTunes and buy digital movie files, but the means to play back these files is limited for your average American.
As for streaming movies, the issue is one of speed. To get good playback of streaming content, you need at least 10mps. I doubt 40% of this country runs that 'fast'. I don't think enough people want to pay for it at current prices.