While replacement of optical discs likely will occur, it won't for 10 or more years. You'll never see the Studios shipping content on flash media because it cannot be pressed, thus production costs for such would skyrocket.
I doubt it. The ISPs will want to get your money for the bandwidth. The cost of that will be added onto the cost of the purchased download. In addition, the Studios aren't too keen on such delivery because it takes the content out of their hands (to an intermediary). They don't like the iTunes Store, but they are biding their time until they can come up with something they can control.
That may be, but it will be with us for a decade or more. There is nothing on the horizon to replace it.
Even with all of that said - Would people here really watch Blu-Ray's on their iMac consistently over a 40"+ TV in their own living room? It's a "nice to have" but certainly not a "must have" to determine whether you should buy an iMac.