"most developers simply lack the writing skills needed to write clear and concise changelogs. ... [M]ost developers can, at least, be trained to write a reasonable impact tag.
Counter to intuition, I understand from a number of people who write for a living, as well as from personal experience, that it is a good deal harder to write something short than something long. Usefully capturing the important details of a patch in a single line is *much* harder than explaining what it does in a couple of paragraphs. Encouraging single-line changelogs scares me.