Interesting article, it might tempt me to try some flats, the last time I tried some was on the MTB it wasn't a good experience my feet kept coming of the pedals, I have never pulled up on the pedal in nearly 60 years of cycling, but I have been using clipless since the early 1980's so any change will be a big one for me.
One things for certain, I wont be cycling in sandles or crocks, stiff sole shoes are fine for me.