That's a fair point - even in tiny tiny Ireland there's many regional dialects, with larger countries there'll typically be far more. I guess the simple answer

That's a fair point - even in tiny tiny Ireland there's many regional dialects, with larger countries there'll typically be far more. I guess the simple answer to that is: how much interest is there in maintenance. I don't think there's any compelling reason not to create something: if there's insufficient interest in maintenance that's an imperfect but reasonable proxy for utility. I'm not aware of any maintained en_US_Xyz languages but it might be pretty cool if someone started. There's precedence in a few other languages, like no_NO_NY, zh_Hans_HK, etc.