I am still not following why Twitch needs to maintain live copies of all the failed runs. Once you hit the objective, make that video the highlight or whatever to be persisted indefinitely.
Why would anyone care about watching several hours of something when they know ahead of time it's not going to be representative of a successful outcome? Iteration #17 out of hundreds can't possibly be valuable enough to justify the storage cost in even the most charitable of cases. It seems to me that most of speed running could be done completely offline without involving the internet and video capture technology (i.e., practicing a musical instrument).