Finally, can we move beyond CD's already
First, I would want the cost to be equal to what current CD's are, or at least very close.
I am glad to see the push towards releasing HD audio, Its about time. MP3's have been a step backwards. I have nice studio monitors and can take advantage of the better audio quality. Practically, 24 bit does make a big improvement over 16 bit when recording, it is kind of like how 10 bit video provides smoother gradients.
There is a level of diminishing returns to how much increasing the sample rate improves perceived quality, 96kHz is great for listening, and a higher sample rate like 192kHz can help with signal processing. Going higher than 192kHz to 384kHz currently costs a substantial sum of money, see Antelope Audio Eclipse 384 Mastering AD/DA Converter, and I do not know of one less expensive either.
One other hidden factor is the clock of the converter, lesser quality clocks will have more clock jitter degrading the audio quality. Very accurate clocks are not cheap see, Antelope Audio Isochrone 10M Ultra Stable Oscillator.