Hmmm? This is a tough one because your product is so wonderfully horizontal, meaning it applies to a very broad set of cases. I'd slice and dice in two directions.

First, I'd think about the general process of collaboration on a document, for example: a) drafting - are two people actually writing the words together? I personally don't like this. b) first read through together staying on the same sentence or page, c) editing together, etc.

Second, I'd think about industries or verticals or contexts, such as in a Legal setting, in a Tech Documentation setting, in a coding or XP dual programming setting, in a social media post drafting setting, and so forth.

Check out: https://medium.com/look-what-i-made/fd48c3b412bc Seems to be evocative of what you're doing, but targeted to one specific use case of "pair programming".