We found one participant being confused by the fact that you can upload only one image by default. Although that's obviously not a significant data point, we felt it was just a weird default anyway.
Although this was a limit we set initially for the Bartik theme, and standard profile in Drupal 7 - there seems no good reason to do this. Users expect to be able to add more images, and requiring them to go deep into Drupal's configuration just to add a few images to an Article
I propose we set it to unlimited.