Ok, so the philosophical "involatility" is preserved, sure, but that's rather a large amount of work to do to preserve unworkable deadends and silly commit messages and broken builds and the like.

Also, it introduces a huge non-linear mess into the commit history that can be hard to untangle. Just looking at topic branches in a normal tree with gitk can be hard. Can you imagine looking at topic branches and these junk branches at the same time?