Another approach would be to implement some form of congestion avoidance in the node selection process. There have been some suggestions in the past around that topic.
The interesting part is that this would solve the problem for customers, but is also a feature often requested by SNOs as it would prevent their nodes from being overloaded.
Multipart uploads will help, but especially if traffic levels increase, it is merely a retry and doesn’t prevent the problem from occurring to begin with. Smarter node selection might.