Having enabled this module, I see in the network traffic that all images for all journal entries are downloaded upon initial load of the system.
When images are large, this can lead to a considerable delay in initial load time for the user.
My suggestion is to resize the images on the server and cache the images. This will allow for all journal entries to have thumbnails without adding megabytes to the initial download screen.
This a great QoL module. Is it going to be upgraded to v10?
I appreciate this may not be feasible due to the new journal model. If an upgrade is not planned, I'll raise a feature request to have the functionality included in core.
As suggested by https://gitlab.com/fohswe , having this as an optional display style for thumbnails to indicate whether a journal entry has an image or text or both.