I remember when I first came across that canon. It also happened to be one of the first set of canons I had read. And, I will say, understanding denzinger and canons becomes much easier after you have read all of them(denzinger from start to finish).
This is complicated for the laity, and it is conceivable that the most complicated clerical matters simply are above the understanding of the laity. And, this canon and its implications is likely in my opinion the most complicated canon to apply. Because, not only is a canon to be understood by its context, but canons also are potent in themselves, transcending the time periods in which they were said, becoming applicable for all time. However, when being applied to situations in which they were not originally intended(in this case originally applied towards to protestants who hated the latin rite and wanted a novus ordo like the church now has, attended by types who have a disdain for the old liturgy and old ways), they lose some of their potency. And, those decisions become prudential decisions, and are best left to the bishop(s), of which +Lefebvre was one. Really, end of discussion. Applying this canon at this point is a prudential decision, and +Lefebvre surely kept this canon in mind when he decided to implement a "liturgy of econe"(1967 liturgy mix and matching the most traditional rubrics allowed), which he is still criticized for. Surely it was this canon that influenced him to experiment saying privately the novus ordo in the early days of the sspx. +Lefebvre was also severely criticized for that at the time by De Lauriers.
My personal opinion about this canon applied to the novus ordo liturgy is that if looked at entirely objectively, which is not realistic, yet sufficient when judging later applications of the letter of the law; in its most traditional "potential" manifestation, aside from the fact that it still causes divisions due to human frailty, its most traditional manifestation(which by the way the church has not seen even fifty years after the council) would pass the test for a catholic generation who had not experienced the revolution of vatican 2 or been formed/attached to 1500 years of a particularly universal liturgy. However, that is not realistic. We not only must be objective, but also subjective. We must be subject(ive), because the church is hierarchical. We are "subject" to authority, which is quite a mystery in itself, because there are checks and balances in the church. We have to be subject in so many ways. With that said, I do not disagree with +Lefebvre/sspx thinking when they say that the novus ordo is bad and should be avoided/abolished. But, at the same time I do not disagree with +Williamson who says if you feel you must attend, you may.
My gripe as a layman has been that tradition(the sspx) has not provided you could say a survival guide for how laity can/should attend the novus ordo if they feel they must(no sspx/ecclesia dei nearby). But, not requiring them to do so. However, even with this lack of, God is not some distant being, he is close, and has provided countless souls with instruction as to how to survive in the novus ordo. So, I do not let my gripe get the best of me. It is a small matter.