Flight length is an issue with me too. My back and legs will not put up with coach seats for anything longer than 3 hours or so. Anything longer and I have to go business or first or I am miserable by the time I arrive. I have to have the extra leg room and more comfortable seat. So, I am not going to fly coach to Europe, Asia, or Australia. Ain't gonna happen. It's my problem, but it still means I'm not flying to China just to take a mainstream cruise. If I'm dropping major money on the air, I'm going lux line all the way, and since they often offer business air specials as part of the cruise, well, that makes it a lot simpler to choose. RCI certainly isn't going to do that with their Choice Air.
Ship2shore is correct - they'll take my money for the Quantum out of China, but it'll be a 'do you really understand what you are getting into' thing, meaning I'd best brush up on my Mandarin even to order room service.