It has been defeated, but through hardware attacks (voltage glitching mostly). The author did an very interesting presentation about the process at reverseconf: https://www.youtube.com/watch?v=FTFn4UZsA5U&t
Amazing video, thanks for sharing! Somehow I missed this entirely when I was researching for the article. Its fascinating seeing the lengths Markus had to go to to wrestle back enough control from Microsoft to glitch the console.