DVD/Blu-ray will still be around long after 2020, Not everywhere will have superfast broadband by the end of the decade. some areas are still only at 2mb/s at most. Others at upto 8mb/s. Releastically for streaming you are talking a minium of 20 mb/s espically if you have more than 1 computer trying to stream.
I also think the days of "all you can eat" broadband are numbered. When providers start to charge for all the extra streaming data that will slow down (or stop) the shift away from DVD/Blu-ray.
Wouldn't people like Hulu, YouTube, and other major streaming services fight tooth and nail to prevent that from happening? At least, I would if I were in their shoes; that's a pretty serious threat to their revenue model.
If the ISP's believe they can make money by charging those companies a fee to have unlimted service they will. Either way the consumer losses out.
After all from an ISP point of view, why should I help anothers company revenue stream, if it'll damage my own.
Of course a solution for those companies would be to become ISP's themselves.