True. Also questions of significance or (unusual) procedure. Gore is not appealing. If Gore has a problem with the result he should appeal. Regular procedure as I understand it means taking Baker and/or Richards, the state could argue or file briefs in those cases and still overrule Peruta. I bet the 9th has left a wrongly decided panel decision stand dozens and dozens of times when a defendant did not appeal, while they waited for right case to take en banc. How many times has a court 1) allowed the AG to intervene at the en banc level at the last minute, 2) after being warned state law was implicated and denying to participate, 3) when the defendant themselves declines to appeal?
Imagine the disarray if federal courts allowed this kind of willy-nilly last minute intervention when states did not like the result, because the defendant was not appealing. Who knows... SCT may look at it for the unusual procedure alone.
To me, this is that moment in poker when your excitement overwhelms your brain. Taking Peruta screams look at me!!! Look this is so important we bent over backwards to take this case!!. I think if she was smart she'd take a deep breath and move to Richards.
I'd take a wild guess and say the 3 scenarios you point out are extremely rare, if ever happening before. The intervention has taken off on a case all its own. As far as Richards she is trying to get involved in that too. I think the state was caught off guard by Gore's bowing out (and the loss) and is now scrambling to get involved because they're afraid Yolo County may not proceed to SCOTUS if they get denied en banc.
There was a good article on en banc and how some judges are asking the question, if the case is good enough for en banc why isn't it good enough for SCOTUS? SCOTUS' function these days is almost exclusively devoted to resolving splits. We see them taking many cases which deal with very technical aspects of the law that just don't touch everyday people, while continually bypassing cases that do affect many people.