Several things caught my attention here:
* Sourdough almost never appears in cookie dough, but this is a great application for it.
* The recipe layers many sour notes including sourdough, key lime, and ricotta cheese. I imagine the results are symphonic.
* Substitute any other citrus you like such as Meyer lemon, Buddha's hand, blood orange, chinotto, etc.
* You might also experiment with other soft cheeses similar to ricotta, or use a cream cheese icing.