Unless they also fork Gtk3 and Gtk4 the GNOME will still seep in and ruin the desktop. Things like gtkfilechooserwidget are terribly broken in gtk3 and gtk4 but at least gtk4 finally got a patch that allows you to paste into a file->open window without it error'ing out. But gtk4 is still firmly in the "no text entry window for you" in file chooser menus by default.

Also, I looked at the github repo for cosmic under pop!_os's stuff and there's no actual code. It's all boilerplate with a single gsettings schema .xml file. There's no DE in that repo.

My favourite “UX bug” is when Discord wants to upgrade, it downloads a newer deb, you open it in App Store, and it only shows the “delete” button. Wonder if it’ll ever be fixed.

current pop_os has image 'previews' in a sidebar as you select images, which isn't the same as a thumbnail but accomplishes much the same purpose

No we don't do that in Linux world, please place "metadata" where it belongs...the inode.