Currently the revision-create and revision-visibility-change event schemas contain fields like rev_content_model and rev_content_format but with multi-content revisions that's not enough cause all the slots might have their own model and format. Also, some other properties might make more sense per-slot.
I suppose that the existing field's documentation should be updated to reflect the fact that these are for the main slot. We might consider doing a backward incompatible change and rename the properties, but it's not advisable. Additional properties should be added to describe other slots as well.