Hi,
I have just joined in, I have been working on finding more perennial brassicas ever since I was given seeds of D'aubenton Kale and now have three young plants (six months old). Hopefully I would be able to share when I have seeds available.
I have a friend who has Sukuma Wiki Kale and they are perennial and has been growing here in Wellington for more than ten years. I recently got seeds of this variety from a different source and will check for perenniality. My friend's Sukuma Wiki flowered but unfortunately he did not save the seeds as I advised him to. Hopefully it flowers again soon, last flowering was three years ago.