Just last week I held a Nix Hour relating to recursion in the module system, and it also covered getting infinite recursion with mkMerge and how to work around it. Feel free to check it out, comes with timestamps 
https://www.youtube.com/live/cZjOzOHb2ow
And if you want something else covered in this format, feel free to ask a question directly by joining, or writing it down in GitHub - tweag/nix-hour: Questions for the weekly Nix Hour beforehand