Yasuo Kobayashi used to say that he was the one who introduced shikko as an exercise - in the 1950's.
People today are paying the price with their knees.
But even at 77 years of age, Yasuo Kobayashi's shikko and suwari practice is better then just about anyone else. Doesn't seem to have crippled him much if at all; so perhaps folks need to take a better look at how he was moving to better understand how to avoid the price of their knees. Somewhere on YouTube there is a video of him explaining a part of these exercises a few years ago, I'll see if I can locate it and post it here.