This feature is enabled (in preview) for Accounts, contacts, cases, and opportunities but for some reason, the Knowledge Article entity was left out. To provide the ability to see Artice version in a roll-up would be very useful for Knowledge Managers and Authors rather than having to use the Related article component which only has limited fields. This would provide a way to easily see all versions of the article and the changes in key fields over time. I can also see a benefit to being able to show key article metadata and roll it up by Subject or category for example where the drill down shows the articles related to a subject.