Hey man,
that’s a great approach, and thanks for even taking the time to prepare and send me a project!
It works pretty well for randomization.
I was wondering how I could “select” a country during gameplay if I don’t have access to the color palette in the Blueprints. But I guess since it is on world coordinates it would be possible to - as you said - feed the cursor location into the material, grab the color underneath it and compare it to the color of the pattern as a whole gut get the cell underneath the mouse… 
IF that works the only other thing is that the blueprint itself would not really be able to work with the shapes as it doesn’t really know the boundaries I guess… hmm
But it gives me a lot to try out 