We can call it the "Dragonborn Canonicity Test." In other words, how do fans of a particular setting react (and why) to the idea of adding Dragonborn to the setting. Because, in general, I think that it potentially showcases how different fan groups often approach their respective settings. For example, adding Dragonborn to Eberron wasn't really all that big of a deal because of the setting's mantra: "If it exists in D&D, it has a place in Eberron" (3e ECSB) and "If it exists in the D&D world, then it has a place in Eberron" (4e EPG and ECG). Eberron exists to be useable for everything plus more. But what about other D&D settings (e.g., Greyhawk, Dark Sun, Ravenloft, etc)? I think we both know what that conversation looks like.