The "re-mastering" comment is (to my way of thinking), key. If I understand the advantages of MQA, it's that the removal of "blur" requires that they go back to the "analog to digital" point in time and fix it at that point, so when the DAC does the "digital to analog" conversion, it's somehow "linked" to that earlier point in time...in the way the DAC does its job.
It would seem to me that the only way to do that would be to "re-master" the music.
I suspect that "re-mastering" is not cheap, so I wonder if the "business case" might preclude most labels from producing much MQA...especially since the majority of people of OK with MP3 on their phones, the hi-quality audio market is just a small sliver of the overall music consumption world.