The JPEG XR format is great. I guess it will take over the "presentation segment", i.e. what JPEG and TIFF is used for today. It could be used for encoding the raw data as well, lossily or losslessly, in smaller storage than the encoding methods are doing that today.
The topic of this thread is not if JPEG XR is better than JPEG. The topic is, if the concept of recording more or less raw data in camera and processing it off-camera remains superior to in-camera processing, or if higher quality recording of the in-camera processed images makes the raw data obsolate. The form of storing the data (encoding) is irrelevant in this question.
The question is, if negative film would become obsolate if the polaroid's quality were better.
Personally, I see the topic of this thread slightly differently. But for the moment, if the question is, "which gives superior results, in-camera or post capture processing", I am in complete agreement that the post-capture results will be at least equivalent but almost always superior, (provided users are willing to use the appropriate tool*) because of a number of factors including, computing horsepower, application sophistication and flexibility.
If we ask the question if the amount of difference in the finished file will be great enough that photographers will, in general, be willing to invest the extra time
for these incremental improvements, my answer changes--working professionals, consumers and most amateurs are unlikely to see or see enough of a difference to care.
I believe that most will not be able to see the difference, or enough of a difference to warrant the traditional raw-camera-processing post capture workflow in a mature JPEG-XR world (years away, I am sure). I foresee the majority of photographers moving on from mosaic'ed formats and not looking back, especially sensor resoloutions as high as they are and still climbing.
So yes, calling it a 'convenience workflow' or a 'presentation format' is all fine--I believe it will become the defacto standard format people use to store, edit and share their files. There will remain people for whom mosaic'ed raw files are not obsolete.
The speculation on adoption is a just a prediction (ie. opinion, not fact) based on experience as I have seen it, nothing more.
* using the appropriate tool properly for optimal image quality can also be a non-trivial task, if one is not technically experienced.