Is there for Vim what Gource is for Git, to visualize Vim undo history?
EDIT: this is only an alternative, not a relevant answer.
You're looking for vim undotree.
It shows the full history tree, and diffs with the current version.
Convert the undo history into a Git repo using Rich's
UndoCommits function, then use something like
gitk to visualize that Git repo's diffs.