Holographic discs will likely be the successor, although the only possible use I can think of is entire TV shows in hi-def on one disc. Would be nice to pop in a Buffy disc and watch the whole thing in HD without having to get up to change the disc. But you can do that with a digital collection too.
I think it's just a matter of time until hard drive capacity reaches the point where I can have my entire media collection on one drive. That's the future, at least for me. I might be buying the discs to display on my shelf, but I'll take sitting on the couch and choosing what I want to watch from a menu any day.