No amount of discovery will uncover the identities of the unnamed defendants. Therefore, by naming as defendants all persons the future President could possibly invite to administer an oath, lead a prayer, or help in the planning of these events, plaintiffs are essentially seeking a declaration of their rights accompanied by an injunction against the world. There is another name for that type of generally applicable relief: legislation. And that’s not within the power of the courts.
I'll have to remember "declaration of rights accompanied by an injunction against the world"; it summarizes in a straightforward way why I think working for rights through the courts doesn't generally work well.