I always expect these kinds of things at the very end of the month. Nintendo has a nack for delivering stuff late. Recently we have been getting downloads early n stuff but I wouldnt hold my breath, just so that the time doesnt drag as much. For me, time slows down when you want something really bad.
I'm assuming it's next week, because after next week it's kind of past "mid-May"... *remembers the 'end of May' update in June, and the 'November update' in December* ... oh wait.