I also vote for export if images. The possibility to include custom images is the main reason why I pay for the Pro version of Dynalist. Often, I could link an image from the web instead, but it is important for me to make sure I never loose the image. The fact that I have no way to extract the images in bulk from Dynalist makes me very uneasy.
It also makes it impossible to migrate/merge different dynalist accounts.
Downloading images as part of the backup would be a solution. A mitigation would be at least including images with export