Interesting blog post, thanks for sharing!
I have a bunch of different fabric markers, I keep intending to do a test like this too but so far...haven't done it.
I'm also wanting to test out using Aunt Martha's ballpoint "embroidery paint" tubes. My gran used those all the time on quilts and dolls for me that have gone through countless washings and still look great. I want to test them out and make sure they haven't changed over the years.