IMHO the LCD-2 at 600-900 bucks are OK, because sound-wise are good, in an enjoyable and fun sounding way. They perform better than many more expensive dynamic offers at similar or higher prices, name the T1 for instance. But for build quality and comfort they're not worth that much.
If all the LCD-3 has to offer is just an improved headband, some sonic benefits (which I really doubt are happening considering most people's comments, Tyll's measurements, and not having evidence the drivers are really different), there's no way I'm spending 2000 USD to try them, not even 1500 on an used pair. To sell at double the price the LCD-2 and being worth to me, I guess this is crucial part of this comment for most people can think otherwise, they'd need to sound clearly deeper (space-wise), more focused, more detailed, "airier" (as in a more extended and better resolved top octave), not having any risk of resonances, echoes or other sound aberrations, and offering a much improved design. Hanging directly from your head by a classic headband a heavy headphone isn't my idea of ergonomics. Sony wouldn't have done that with the R10, and didn't with the lighter CD3000, nor is doing Stax. $2000 should buy you a decent, well built and comfortable frame.