Juche
Juche officially replaced Ko Dang in the 1980s, and is practiced by most ITF-related schools today. Many who claim to practice Ko Dang, in fact, are only practicing Juche under a different name. If your "Ko Dang" has a bunch of ridiculous kicks, jumps, and jump-kicks, you are practicing Juche.
I do not practice Juche. I have never learned Juche, and I have no desire to. I may come back to examine it in the future for this project, but that is not a priority at the moment. It is the youngest of the Chang Hon patterns, and therefore the furthest possible from Taekwon-Do's Karate roots, and I doubt it has many similarites to Karate kata to begin with. It's historical significance is in the circumstances surrounding its creation.
"Juche" is the name of Kim Il-Sung's North Korean political ideology. It is often taught in Taekwon-Do dojangs as meaning "self-reliance" or some such, and while the word may literally mean that, it is the official ideology of the North Korean Kim regime and only exists in the syllabus because of the ITF's connection with North Korea in the 1980s.
Why did Choi Hong Hi want to connect with North Korea?
This is a question that has many answers. Some say it is because he was born in the Northern part of Korea before the split and had an affinity for his home. Some say he wanted to see Korea reunified, and he believed that this meant cooperation with both North and South. He later wrote of wanting to connect the whole world, communist and otherwise, though some see this as a post-hoc justification for his dealings with North Korea.
Others say that he wanted legitimacy for the ITF, and since the Kukkiwon, the ITF's main competitor in Taekwon-Do, was part of the South Korean government, he would have to turn to the North if he wanted more "official" prestige. Some say he was running out of Koreans and couldn't go to South Korea for them because of his self-imposed exile.
Regardless, after connecting the ITF with North Korea, Ko Dang was replaced with a pattern named after Kim Il-Sung's personal* ideology.
Why replace Ko Dang?
The total of 24 patterns has a symbolic meaning, so Choi could not simply add a new pattern. Choi's official explanation was that the Chang Hon pattern series was missing techniques, and he needed to replace Ko Dang with a pattern that contained more techniques to "complete" the pattern set.
"Ko Dang" was the pen-name of Cho Man-Sik, one of the early potential leaders of North Korea. As a popular figure of resistance against the Japanese, the Soviet Union hoped they could influence him and make North Korea as a Soviet-friendly country. Cho was opposed to this, and while he maintained some power in North Korea, he was eventually imprisoned and murdered so the Soviet-friendly Kim Il-Sung could seize power. Some say it was Kim himself that had Cho executed, though it is impossible to know.
Ko Dang Tul represented a direct political opponent of Kim Il-Sung, so if the ITF wanted a relationship with North Korea, Choi felt that it must be replaced with a pattern designed to pander to Kim.
*Kim himself did not actually create this idea, and had little (if any) actual involvement in its development.