@theluthier
There is a few other ways to show background images in 2.8.
https://blender.stackexchange.com/questions/110532/cannot-find-background-images-feature-in-blender-2-8
When it comes to skextchfab they say that it probably is because the addon needs an update, but it might work to upload the file with the upload button on sketchfab allthough it didnt work for me.