Not right away, I don't think
There are people a lot more plugged into this technology than I am, but my understanding is that many if not most Blu-Ray players also play standard DVDs.
But...let's face it, if the entertainment industry can get you to replace your movie collection with newly-purchased disks, I'm sure they'll do just that. The name of the game is to make you fork over as much of your money as possible, after all.