When you update an article and click "Notify Followers", why not add a little text field somewhere where you can type in what you changed?That way, it would appear in the notifications. The little box would contain the comment below its main text. So the followers would immediately know what was changed.Mockup of what the notifications would look like:

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OPTIONAL ADD-ON: Those comments get added somewhere on the bottom of the article (maybe Metadata section) automatically with a timestamp as well, creating an automatic changelog.