Look at two other consumer trends:
There was a time when people sat down and listened to music. Today, people just download compressed music. there are always going to be audiophiles, but they are the minority. I'm one of them, but I know it's not the norm.
Then there is Blu-ray. Where can you rent those today? How big is the Blu-ray section in your local electronics retailer? Again, I've got a movie set-up at home, but I'm the minority. I didn't think people would ever watch movies and video on small screens, but it's happening.
On one side, we have quality...image quality, video quality, sound quality. On the other side, we have convenience, weight, on-demand, cost, etc. I don't know if SLRs will diminish in sales numbers, but for all those that don't think it's even a remote possibility, those people aren't looking outside of their own world.