First bit of this proposal : https://devtalk.blender.org/t/new-slots-system-in-render-view/731/14
At the moment I set up the buttons so it made me play a bit with the code, now I am working on having a functional "Push" button.
[x] UI buttons
[x] Offset all the slots with the Push button
[x] Make Auto Push after render work
[x] Change slot attribute when toggle "Compare With"
[] Implement the different comparison modes
[] Add icons in the slots lists
[] Add preview thumbnails to the slots list
Known issues:
[] Toggle "Compare With" should have a default value of 1 and it shouldn't reset when we close the Image Editor
[] Crash sometimes when trying to display a slot
[] Reload Start-Up file after having pushed renders in frame buffer