Plugin based on Tile Preview by Jakub Neruda.
Source code Tile Preview:
https://github.com/nerudaj/gimp-pixel-a ... 3/plug-ins

This is what Tile Preview looks like:


I encouraged the plugin author to create a simplified version of Tile Preview only to display a second preview window of the selected layer - which seems useful to me when working in 'Single-Window Mode'.
Maybe the author will publish it someday.
My temporary version is very experimental (created for the purpose of learning gtk3) because the code can definitely be cleaned up more and alpha channel support added (which is missing in this version).
I wonder if this plugin will be useful for You?

In menu: Tools ➤ Second Preview

A very interesting idea MareroQ.