Canon is in a bit of an awkward position, it seems.
First, I'm sure that, eventually, DO will be everywhere. I can easily imagine even moderate focal length lenses getting the DO treatment to turn them into fast pancakes.
But it's obviously not easy doing it with today's technology.
What's worse...well, anybody willing to blow big bucks on a Great White isn't interested in compromising image quality. The IQ hit the 400 DO takes...well, why bother if the 400 f/5.6 at a stop higher ISO gives better IQ with the same shutter speed for a fraction of the price and the weight?
So, until Canon can get the image quality of a DO lens not only on a par with their other Great Whites but even a step ahead, it's going to continue to be the redheaded stepchild of the imaging world.
But, in the mean time, they've still got to keep making the things and basically not selling them. Doesn't make for a very easy path from here to there.