Currently VisualEditor can load a single revision of a page from Mediawiki. However sometimes we would like VisualEditor to load a changeset from Mediawiki instead.
A changeset means the differences that take the page from some revision X to some other revision Y. Loading it into VisualEditor can be thought as the inverse of clicking the Publish button: the editor state would be similar to if the user had loaded up revision X and then made the changes so the page looks like revision Y. Currently we don't have any way to do this: once the user publishes the page and closes the VisualEditor session, we have no way to get back to the state just before they clicked publish.
The changeset would be available in the same format as the edit session history (technically a ve.dm.Change object), and software such as Edit Check could examine the changeset and react accordingly.
This building block could be useful in a wide variety of cases, e.g.: