Right, shoot for 20mins and instead of swapping memory card, swap cameras. Sure the pocket is deep, but have 10, 20, 30 of these lined up? What kind of workflow is that? It's absurd. It's not about cost, its about efficiency.
The truth is 8k is not useful for the wedding crowd (yet), look, I said the word YET!!! see it? just in case, I said YET.
The people who can take advantage of the 8k, its niche. Canon didn't make this for niche, however 8k is impressive, impressive that they have pulled it off and for that they deserve credit, and it will create some halo effect for the brand. In practice however, it will be limited in use.
I am sure there will be lots of people shooting home movies and little projects with it, 30seconds clips here and there, long set ups in between and it won't bother them. They wouldn't notice the heat even. For a long shoot, you just can't have something that would overheat.