WeWrite will have a one-click "Save" flow. MediaWiki, in contrast, has a two-click flow which prompts users with a confirmation + change summary.
Pages should always be editable (to encourage editing) like in Apple Notes.
Perhaps a "live diff view" could be used while editing, so as to show the user what's they'e about to add and delete. Maybe this could be a toggle option.
The changes and change summary will be available somewhere in the UI, whether as a floating element or at the bottom of the page. This means users can skip filling out a change Summary if they so choose. (These could be filled out later, if need be)