Personally I expect the prices for this sort of device to rapidly fall, especially if streaming video capabilities are included. (Video matters a lot less to me, but more so to the general population, I bet). I predict that the equivalent of the current SB3 will be selling for $50 in two or three years. That said, I'm very glad I own my SB3 now-I use it extensively and when I get around to it will probably box up my CDs.
But I wouldn't dismiss the notion of a $2,000 SB4 completely. Look at the vast number of extremely overpriced audiophile products that are out there. But at $2,000 it would definately be a niche product.