Yes they are expensive - but so were BD Burners, DVD Burners, CD Burners, HDD, and so on and so forth when they first came out. The question is do you need the kind of performance these would give?
The more I read, the more I find that HD video editing benefits from source disks that can maintain their throughput speeds. Hard disks drop in performance while SSDs sustain their speeds. That is one scenario where these would benefit (and if you are willing to drop $3k to $150+k on a camera, what is a few thousand for some source drives).