Shipwreckedcrew has a good article commenting on how inadequate the PA response was: Pennsylvania's Response Ordered by Justice Alito Reflects Fear of the Defendants About What Might Be Coming. The article was written, of course, before the SCOTUS dropped that particular ball.
Here's how silly he finds the legal arguments, in a nutshell:
The idea that the Supreme Court should shrink from making difficult choices in reaching a decision in a case before it due to the claim by Pennsylvania that no court has ever done this before is moronic. Yes, it’s never been done before.
Also yes — no State has ever conducted an election in a manner that violated the State’s own Constitution.
OTOH, he closes the article this way--and it reflects what probably happened:
The one issue raised by the Response which I think might resonate with the Court is that any decision which inserts the Court into the determination of Pennsylvania’s Electors runs contrary to “separation of powers” principles which place the responsibility for resolving disputes over the validity of named “Electors” with Congress. ...
This raises the point that I made in my article yesterday — how is the Court prepared to respond if it were to grant the injunction against the Pennsylvania state defendants, and on January 6, 2021, the Joint Session of Congress nevertheless counts the slate of Electors already certified and sent by the Pennsylvania Governor for Joe Biden?
There is no functional method I can envision where the Court would attempt to place itself deeper in this controversy between January 6 and January 21 if the Congress was to certify the vote of the Electoral College which included 20 Electoral votes from Pennsylvania in favor of Joe Biden. ... I think there is no question that the Democrats, in their overriding desire to be rid of Donald Trump and deny him a second term, will disregard the damage they would do to the Court by ignoring any Order and moving forward. ...
Damage to the SCOTUS? How about damage to the Constitution and the nation?
What this means is that the SCOTUS will be de facto acquiescing to a federal election system that it tacitly acknowledges is broken beyond repair. In other words, to a broken US Constitution.
That is, unless the SCOTUS tries to address this mess through the other cases.
UPDATE: Commenter aNanyMouse quotes SWC--after the news came out--saying:
"if the Court was truly seeking to “wash its hands” of all election controversies involving Pennsylvania, it could have said so today, in statements accompanying this Order. By playing “coy” in giving no reason today, it did nothing to “tip its hand” about the sentiment inside the Court, on the actions of the Pennsylvania Supreme Court and state officials, across a host of issues.
That's a fair take, it seems to me. It also tells the many commenters who are asking, What does it MEAN? about all that we can say: They don't want to tip their hand. Most of the views expressed in the comments remain possible. It does seem that if the SCOTUS had really intended to "wash their hands" of all the election controversies, not only COULD they have said so, but really in fairness to all concerned parties--which would embrace the entire country--they SHOULD have said so.
My view, as already expressed, is that this is not simply a legal matter--it's a political matter in the big picture meaning of the word, involving all three Constitutional branches of government, co-equal and intended to balance one another. I believe that at least five of the justices truly want to reach a balanced resolution and are appalled at what they know has transpired. They know that our constitutional order is up for grabs. But as a constiutional institution seeking to preserve that constitutional order they can't simply go on gut convictions--as commenter EZ indicated, they're searching for the right way to come to grips with this crisis that is in harmony with the order they want to preserve. Is the Texas case the way forward? Maybe. Is there something else that we don't know about? Maybe.
It's not a satisfactory position for us to be in.