Is it possible to add change listeners to a certain chunk in the document, that when it changes it would trigger an event in JavaScript and notify the add-in using Office.js?
An example would be selecting a paragraph and adding a listener, which upon the paragraph change, the add-in would get notified.
If yes - which API method (office.js) should be used in which requirement set? If not - are there any plans of developing something like this?
The Word JavaScript APIs do not support any events for paragraphs or ranges. But it's a good idea. Please go to Office Developer suggestion box and search for "word events". Vote up any suggestions that match your needs, or create a new suggestion.