While I agree with the article's point, we should note that collisions do not happen out of the box because Neovim defaults undodir to $XDG_STATE_HOME/nvim/undo/ (~/.local/state/nvim/undo/), while Vim defaults to storing .un~ files alongside the edited file or inside ~/.vim/undo/. Data loss only occurs if both editors are configured to share an undo directory or save inline .un~ files.