Breviter: Two things Bp. D'Arcy couldn't do re Notre Dame
This matter is not simple and my analysis of it would not lend itself to blog-style discussion anyway. But, for the benefit of readers who have asked, I can at least take two options off the table. Briefly:
1. The local bishop cannot put Notre Dame under a local interdict, even for a brief period, if for no other reason (and there would be other reasons) than that local interdict is not a penal option under the 1983 Code. While local interdict (and community interdict, its cousin) were possible under the Pio-Benedictine Code (see 1917 CIC 2268-2277), today, interdict is a purely personal penalty, meaning that only specific individuals, convicted of a canonical crime, can be interdicted (1983 CIC 1332).
2. The local bishop cannot forbid the celebration of Mass in campus oratories and chapels by a precept under 1983 CIC 1225. While the argument here rests more on scholarly opinion than does that above, I think the weight of that opinion would not support a bishop's using a precept to forbid Mass on campus during graduation weekend.
Mind, nothing in Bp. D'Arcy's statement today suggested that he was considering either option, but my advice to folks who have been considering suggesting them would be to save your time: neither action would be supportable under 1983 Code.
Salvo sapientiorum iudicio.