I had a feeling that the flare caused by FP/DO elements meant that Canon and Nikon would not use them on top tier telephoto lenses. They are used instead on slower telephotos, such as the AFS 300/4 PF and Canon 400/4 DO.
The are are also bokeh issues; the 300/4 PF is not that great in areas in front of the focused subject. I think the fast tele primes are used by people who are very demanding in terms of all aspects of image quality and the weight savings on fast lenses would be less pronounced than on smaller aperture versions.
I do use the 300 PF a lot; it has its advantages and disadvantages. Sometimes the results are excellent, but conventional refractive optics designs are better when it comes to dim, low contrast light, in my experience.
I would expect a fluorite version of the 300/2.8 in the near future.
PF would be highly useful on a lens like a 400/5.6, if Nikon ever decides to make one...
Or a 500/5.6 maybe. I think 300 and 400 are too close to each other to use as a pair but 300 and 500 would be great.