Not for a while
I too can't see how this can be realistic in the near future. I live in an area with reasonable broadband, getting on for 8mb, and I can't stream bluray quality movies over XBL at all, and even when one day I get 20mb broadband, when kids are in th bedroom playing online games, and missus in the kitchen doing her online shopping, i'll still not be able to stream my movie.
I only own a couple of blurays, but I rent them all the time from Lovefilm, and any movies I feel good enough to want to keep I do buy on Bluray, and for something to 'keep' I think people will always want to go to the shop and get something tangible.
I guess it's compared to how music has gone, but I think that has been pushed more by the portability of it, and also music is a far lighter bandwidth requirement.