With all due respect, I really believe you are mistaken on this. So far, I have asked two other priests and they both said the same thing. The Immaculate Conception this year ends the evening of Saturday, December 8, not at midnight on December 9. Counting Fr. David and myself, that is four priests who come down on this side of the debate, and I’m certain I could find more. Now, I’m not suggesting that we somehow know more than your average lay person. I’ve studied both canon law and liturgy, but I would not consider myself an expert in either field. There are many lay people who know far more than me in these respective fields. But, I like to think that the eight years I spent in seminary count for something.
Frankly, I hope that you are correct, because the reality is that many, if not most, Catholics will neglect this very serious obligation. But again, it seems to me and the other priests with whom I’ve spoken, that the canon in question is addressing things like weddings on a Sunday. For what it’s worth, if any of my brother priests have time to celebrate a nuptial Mass on a Sunday, they can come help in my parish

. The canon also seems to address those who may go to Mass in another rite, or in the Extraordinary Form, either or which may be celebrating a different feast with different readings.
But the question here is NOT must one go to the Mass of the day to satisfy the obligation, (which, clearly, the answer is no. I don’t think anyone is disputing that.) but must one go to Mass on the actual day of the feast? Again, it seems clear that you must. The further question then is, when does the feast end? Everything I have read and everything I have studied in liturgical law suggest that the feast ends on the evening of December 8.
Again, I could be wrong. I’d like to see something authoritative from the CDW. I looked a little bit yesterday and couldn’t find anything in either direction.