To add to the confusion, if the Immaculate Conception falls on a Saturday or a Monday the obligation remains. Therefore, this year (because the Solemnity of the Immaculate Conception is on Saturday) the obligation to attend Mass either on the vigil or the day stands.
Of course, the minimalists still have opportunity to do as little as possible. The question has been asked, "If I go to a Mass on Saturday evening, can it count for the Solemnity and for Sunday, too?" I don't even want to answer the question. Besides, it's a non-question in this parish. We have no Saturday evening Mass.
To me, all of this is just a reminder of how some Catholics think. "What's the least I have to do?" And without being unkind or disloyal, I think the bishops have assisted in cultivating that kind of thinking.